Combinations of PDE1 inhibitors and NEP inhibitors

ABSTRACT

The invention relates to the combination of inhibitors of phosphodiesterase 1 (PDE1) and inhibitors of Neprilysin (NEP) useful for the treatment of certain cardiovascular diseases or related disorders, e.g., hypertension, congestive heart disease, and post-myocardial infarction. In another embodiment, the invention relates to the combination of inhibitors of PDE1 and inhibitors of NEP for the treatment of diseases or disorders characterized by disruption of or damage to various cGMP/PKG mediated pathways in the cardiovascular system (e.g., in cardiac tissue or in arterial smooth muscle).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. divisional application of U.S. application Ser. No. 14/820,323, filed Aug. 6, 2015, which claims priority to and the benefit of U.S. Provisional Application No. 62/034,665, filed on Aug. 7, 2014, the contents of each of which are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The field relates to the combination of inhibitors of phosphodiesterase 1 (PDE1) and inhibitors of Neprilysin (neutral endopeptidase or NEP) useful for the treatment of certain cardiovascular diseases and related disorders, e.g., hypertension, congestive heart disease, and post-myocardial infarction. The field further relates to the administration of inhibitors of phosphodiesterase 1 (PDE1) in combination with inhibitors of NEP for the treatment of diseases or disorders characterized by disruption of or damage to certain cGMP/PKG mediated pathways in the cardiovascular system (e.g., in cardiac tissue or in vascular smooth muscle).

BACKGROUND OF THE INVENTION

Heart disease is a chronic and progressive illness that kills more than 2.4 million Americans each year. There are approximately 500,000 new cases of heart failure per year, with an estimated 5 million patients in the United States alone having this disease. Early intervention is likely to be most effective in preserving cardiac function. It would be most desirable to prevent as well to reverse the morphological, cellular, and molecular remodeling that is associated with heart disease. Some of the most important indicators of cardiac risk are age, hereditary factors, weight, smoking, blood pressure, exercise history, and diabetes. Other indicators of cardiac risk include the patient's lipid profile, which is typically assayed using a blood test, or any other biomarker associated with heart disease or hypertension. Other methods for assaying cardiac risk include, but are not limited to, an EKG stress test, thallium stress test, EKG, computed tomography scan, echocardiogram, magnetic resonance imaging study, non-invasive and invasive arteriogram, and cardiac catheterization.

Pulmonary hypertension (PH or PHT) is an increase in blood pressure in the pulmonary artery, pulmonary vein, and/or pulmonary capillaries. It is a very serious condition, potentially leading to shortness of breath, dizziness, fainting, decreased exercise tolerance, heart failure, pulmonary edema, and death. It can be one of five different groups, classified by the World Health Organization as follows:

WHO Group I—Pulmonary Arterial Hypertension (PAH)

a. Idiopathic (IPAH)

b. Familial (FPAH)

c. Associated with other diseases (APAH): collagen vascular disease (e.g. scleroderma), congenital shunts between the systemic and pulmonary circulation, portal hypertension, HIV infection, drugs, toxins, or other diseases or disorder.

d. Associated with venous or capillary disease

Pulmonary arterial hypertension involves the vasoconstriction or tightening of blood vessels connected to and within the lungs. This makes it harder for the heart to pump blood through the lungs, much as it is harder to make water flow through a narrow pipe as opposed to a wide one. Over time, the affected blood vessels become both stiffer and thicker, in a process known as fibrosis. This further increases the blood pressure within the lungs and impairs pulmonary blood flow. In addition, the increased workload of the heart causes thickening and enlargement of the right ventricle, making the heart less able to pump blood through the lungs, causing right heart failure. As the blood flow through the lungs decreases, the left side of the heart receives less blood. This blood may also carry less oxygen than normal. Therefore it becomes more and more difficult for the left side of the heart to pump to supply sufficient oxygen to the rest of the body, especially during physical activity.

WHO Group II—Pulmonary hypertension associated with left heart disease

a. Atrial or ventricular disease

b. Valvular disease (e.g. mitral stenosis)

In WHO Group II pulmonary hypertension there may not be any obstruction to blood flow in the lungs. Instead, the left heart fails to pump blood efficiently out of the heart into the body, leading to pooling of blood in veins leading from the lungs to the left heart (congestive heart failure or CHF). This causes pulmonary edema and pleural effusions. The fluid build-up and damage to the lungs may also lead to hypoxia and consequent vasoconstriction of the pulmonary arteries, so that the pathology may come to resemble that of Group I or III.

WHO Group III—Pulmonary hypertension associated with lung diseases and/or hypoxemia

a. Chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD)

b. Sleep-disordered breathing, alveolar hypoventilation

c. Chronic exposure to high altitude

d. Developmental lung abnormalities

In hypoxic pulmonary hypertension (WHO Group III), the low levels of oxygen may cause vasoconstriction or tightening of pulmonary arteries. This leads to a similar pathophysiology as pulmonary arterial hypertension.

WHO Group IV—Pulmonary hypertension due to chronic thrombotic and/or embolic disease

a. Pulmonary embolism in the proximal or distal pulmonary arteries

b. Embolization of other matter, such as tumor cells or parasite

In chronic thromboembolic pulmonary hypertension (WHO Group IV), the blood vessels are blocked or narrowed with blood clots. Again, this leads to a similar pathophysiology as pulmonary arterial hypertension.

WHO Group V—Miscellaneous

Treatment of pulmonary hypertension has proven very difficult.

Antihypertensive drugs that work by dilating the peripheral arteries are frequently ineffective on the pulmonary vasculature. For example, calcium channel blockers are effective in only about 5% of patients with IPAH. Left ventricular function can often be improved by the use of diuretics, beta blockers, ACE inhibitors, etc., or by repair/replacement of the mitral valve or aortic valve. Where there is pulmonary arterial hypertension, treatment is more challenging. Lifestyle changes, digoxin, diuretics, oral anticoagulants, and oxygen therapy are conventional, but not highly effective. Newer drugs targeting the pulmonary arteries include endothelin receptor antagonists (e.g., bosentan, sitaxentan, ambrisentan), phosphodiesterase type 5 inhibitors (e.g., sildenafil, tadalafil), prostacyclin derivatives (e.g., epoprostenol, treprostinil, iloprost, beraprost), and soluble guanylate cyclase (sGC) activators (e.g., cinaciguat and riociguat). Surgical approaches to PAH include atrial septostomy to create a communication between the right and left atria, thereby relieving pressure on the right side of the heart, but at the cost of lower oxygen levels in blood (hypoxia); lung transplantation; and pulmonary thromboendarterectomy (PTE) to remove large clots along with the lining of the pulmonary artery. Heart failure and acute myocardial infarction are common and serious conditions frequently associated with thrombosis and/or plaque build-up in the coronary arteries.

Hypertension accounts for 9.4 million cardiovascular deaths annually worldwide. The disease affects more than two-thirds of people 65 years of age or older. The effective treatment of hypertension has been shown to reduce the risk of morbidity and mortality associated with elevated blood pressure, including stroke, ischemic heart disease, heart failure, and chronic kidney disease. Despite the availability of multiple drug classes of diverse mechanisms of action to treat hypertension, hypertension remains an inadequately controlled disease, especially systolic hypertension.

In young people, hypertension is predominantly due to increased diastolic blood pressure and increased mean arterial pressure, whereas in older patients, hypertension is primarily due to increased systolic blood pressure due to a loss of elasticity in large arteries such as the aorta. In older patients, the diastolic blood pressure may also drop, resulting in increased pulse pressure, independent of changes in mean arterial pressure. Control of systolic blood pressure remains the most important unmet need in the clinical management of hypertension.

The final common pathway of cardiovascular disease is heart failure, which is often mediated by progressive uncontrolled hypertension. The recent ALLHAT study found that the development of heart failure in hypertensive patients was a powerful predictor for increased mortality.

Cardiovascular disease or dysfunction may also be associated with diseases or disorders typically thought of as affecting skeletal muscle. One such disease is Duchenne muscular dystrophy (DMD), which is a disorder that primarily affects skeletal muscle development but can also result in cardiac dysfunction and cardiomyopathy. DMD is a recessive X-linked form of muscular dystrophy, affecting around 1 in 3,600 boys, which results in muscle degeneration and eventual death. The disorder is caused by a mutation in the dystrophin gene, located on the human X chromosome, which codes for the protein dystrophin, an important structural component within muscle tissue that provides structural stability to the dystroglycan complex (DGC) of the cell membrane. While both sexes can carry the mutation, females rarely exhibit signs of the disease.

Patients with DMD either lack expression of the protein dystrophin or express inappropriately spliced dystrophin, as a result of mutations in the X-linked dystrophin gene. Additionally, the loss of dystrophin leads to severe skeletal muscle pathologies as well as cardiomyopathy, which manifests as congestive heart failure and arrhythmias. The absence of a functional dystrophin protein is believed to lead to reduced expression and mis-localization of dystrophin-associated proteins including Neuronal Nitric Oxide (NO) Synthase (nNOS). Disruption of nNOS signaling may result in muscle fatigue and unopposed sympathetic vasoconstriction during exercise, thereby increasing contraction-induced damage in dystrophin-deficient muscles. The loss of normal nNOS signaling during exercise is central to the vascular dysfunction proposed to be an important pathogenic mechanism in DMD. Eventual loss of cardiac function often leads to heart failure in DMD patients.

Currently, there is a largely unmet need for an effective way of treating cardiovascular disease and disorders (e.g. congestive heart disease, hypertension and post-myocardial infarction) and diseases and disorders which may result in cardiac dysfunction or cardiomyopathy (e.g., Duchenne Muscular Dystrophy). Improved therapeutic compositions and methods for the treatment of cardiac conditions and dysfunction are urgently required. Effective treatments for heart failure with preserved ejection fraction (HF-PEF) are particularly needed.

Eleven families of phosphodiesterases (PDEs) have been identified but only PDEs in Family I, the Ca²⁺/calmodulin-dependent phosphodiesterases (CaM-PDEs), which are activated by Ca²⁺/calmodulin and have been shown to mediate the calcium and cyclic nucleotide (e.g. cGMP and cAMP) signaling pathways. The three known CaM-PDE genes, PDE1A, PDE1B, and PDE1C, are all expressed in central nervous system tissue, as well as in heart, lung, and smooth muscle to varying degrees. PDE1A is expressed in the brain, lung and heart. PDE1B is primarily expressed in the central nervous system, but it also detected in the heart, is present in neutrophils and has been shown to be involved in inflammatory responses of this cell. PDE1C is expressed in olfactory epithelium, cerebellar granule cells, striatum, heart, and vascular smooth muscle. PDE1C is a major phosphodiesterase in the human cardiac myocyte.

Of all of the PDE families, the major PDE activity in the human cardiac ventricle is PDE1. Generally, there is a high abundance of PDE1 isoforms in: cardiac myocytes, vascular endothelial cells, smooth muscle cells, fibroblasts and motor neurons. Up-regulation of phosphodiesterase 1A expression is associated with the development of nitrate tolerance. Kim et al., Circulation 104(19:2338-2343 (2001). Cyclic nucleotide phosphodiesterase 1C promotes human arterial smooth muscle cell proliferation. Rybalkin et al., Circ. Res. 90(2):151-157 (2002). The cardiac ischemia-reperfusion rat model also shows an increase in PDE1 activity. Kakkar et al., can. J. Physiol. Pharmacol. 80(1):59-66 (2002). Ca²⁺/CaM-stimulated PDE1, particularly PDE1A has been shown to be involved in regulating pathological cardiomyocyte hypertrophy. Millet et al., Circ. Res. 105(10):956-964 (2009). Early cardiac hypertrophy induced by angiotensin II is accompanied by 140% increases in PDE1A in a rat model of heart failure. Mokni et al., Plos. One. 5(12):e14227 (2010). Inhibition of phosphodiesterase 1 augments the pulmonary vasodilator response to inhaled nitric oxide in awake lambs with acute pulmonary hypertension. Evgenov et al., Am. J. Physiol. Lung Cell. Mol. Physiol. 290(4):L723-L729 (2006). Strong upregulation of the PDE1 family in pulmonary artery smooth muscle cells is also noted in human idiopathic PAH lungs and lungs from animal models of PAH. Schermuly et al., Circulation 115(17)2331-2339 (2007). PDE1B2, which is present in neutrophils, is up-regulated during the process of differentiation from neutrophils to macrophases. Bender et al., PNAS 102(2):497-502 (2005). The differentiation of monocytes to macrophage, in turn, is involved in the inflammatory component of heart disease, particularly atherothrombosis, the underlying cause of approximately 80% of all sudden cardiac death. Willerson et al., Circulation 109:II-2-II-10 (2004).

Cyclic nucleotide phosphodiesterases down-regulate intracellular cAMP and cGMP signaling by hydrolyzing these cyclic nucleotides to their respective 5′-monophosphates (5′AMP and 5′GMP), which are inactive. PDE1A and PDE1B preferentially hydrolyze cGMP over cAMP, while PDE1C shows approximately equal cGMP and cAMP hydrolysis. cAMP and cGMP are both central intracellular second-messengers and they play roles in regulating numerous cellular functions. In the cardiac myocyte, cGMP mediates the effects of nitric oxide and atrial natriuretic peptide (ANP). Each cyclic nucleotide has a corresponding primary targeted protein kinase, PKA for cAMP, and PKG for cGMP. PKG acts as a brake in the heart, and is capable of countering cAMP-PKA mediated contractile stimulation and inhibiting hypertrophy. Importantly, the duration and magnitude of these signaling cascades are determined not only by generation of cyclic nucleotides, but also by their hydrolysis catalyzed by phosphodiesterases (PDEs). PDE regulation is quite potent—often suppressing an acute rise in a given cyclic nucleotide back to baseline within seconds. It is also compartmentalized within the cell, so that specific targeted proteins can be regulated by the same “generic” cyclic nucleotide. By virtue of its modulation of cGMP in the myocyte, PDE1 participates in hypertrophy regulation. (Circ Res. 2009 November 6; 105(10): 931.)

PDE1 has been shown to be up-regulated in early cardiac hypertrophy induced by the pro-hypertensive hormone angiotensin II (Ang-II), and to be up-regulated in pulmonary smooth muscle cells in animal models of pulmonary hypertension and in human patients. The reasonably selective PDE1 inhibitor dioclein has also been shown to induce PKG-dependent vasodilation, while other PDE1 inhibitors have been shown to reduce lung vascular remodeling and right heart hypertrophy in animal models.

Neutral endopeptidase, also known as Neprilysin or NEP (EC 3.4.24.11), is a type II integral membrane zinc-dependent metalloendoprotease that cleaves a variety of short peptide substrates. In mammals, NEP is widely expressed, including in the kidney, lung, endothelial cells, vascular smooth muscle cells, cardiac myocytes, fibroblasts, adipocytes and brain. The highest concentrations are found in the proximal renal tubules of the kidney. Among its natural targets are cardiac atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), C-type natriuretic peptide (CNP), angiotensin I (Ang-I), angiotensin II (Ang-II), bradykinin (BK), and endothelin (ET). Cleavage of these peptides by NEP results in their inactivation, attenuating the peptides' natural biological effects.

ANP, BNP and CNP are all part of the natriuretic peptide (NP) system, which, along with the renin-angiotensin system, is a major component of mammalian blood pressure homeostasis. While the renin-angiotensin system is primarily responsible for increasing blood pressure (e.g., by promoting vasoconstriction and water retention), the natriuretic peptide system is primarily responsible for decreasing blood pressure (e.g., by promoting vasodilation and natriuresis). ANP and BNP are both powerful vasodilators and strong promoters of decreased renal reabsorption of sodium and water in a potassium-sparing manner. These dual effects exert a powerful blood pressure lowering effect. BNP and CNP also exert an anti-fibrotic effect and an anti-hypertrophic effect in the heart. CNP shares the vasodilatory effects of ANP/BNP but without the renal effects. In addition, both hypertension and obesity have been shown to be associated with reduced ANP and BNP levels, and a specific genetic variant of ANP (rs5068), which increases ANP levels, has been shown to protect against hypertension and metabolic syndrome. Thus, ANP, BNP and CNP play an important role in blood pressure homeostasis and cardiovascular health.

Inhibition of NEP results in an increase in the half-lives of circulating ANP, BNP and CNP. This is expected to prolong their blood-pressure lowering and cardiac health improving effects. Urine cAMP levels are significantly elevated after systemic administration of NEP inhibitors.

Inhibition of NEP also results in higher levels of bradykinin, angiotensin I, angiotensin II and endothelin. Importantly, endothelin and angiotensin II are strongly pro-hypertensive peptides. Thus, NEP inhibition alone results in both vasodilatory effects (from the NPs) and vasoconstrictive effects (from increased Ang-II and ET). These pro-hypertensive peptides all operate via binding to G-protein coupled receptors (GPCRs). The major contributor to this vasoconstrictive effect is Angiotensin-II, which operates via binding to the G-protein coupled receptors AT₁ and AT₂. These receptors exert their physiological effects through activation of phospholipase C (PLC) and protein kinase C (PKC) signaling cascades. Bradykinin is inactivated to a large extent by angiotensin converting enzyme, and ACE inhibitors cause congestion as a major side effect that is not seen with NEP inhibitors.

ANP, BNP and CNP all function via the second messenger cGMP. ANP and BNP bind to membrane-bound guanylyl cyclase-A, while CNP binds to guanylyl cyclase B. Both of these enzymes increase intracellular cGMP in response to receptor binding. The increased cGMP concentration activates protein kinase G (PKG) which is responsible for exerting the downstream biological effects of the natriuretic peptides.

Several NEP inhibitors are known, including candoxatril, candoxatrilat, omapatrilat, gempatrilat, and sampatrilat. Candoxatril had been shown to produce a dose-dependent increase in both plasma ANP and cGMP levels, and although it is safe, it does not produce a stable blood-pressure lowering effect. This is thought to be due to the effects of NEP inhibition on BK, ET and Ang-II breakdown. Candoxatril treatment in patients with heart failure has been shown to increase levels of endothelin significantly, thus cancelling out the blood pressure effects caused by increased ANP.

In contrast to candoxatril and candoxatrilat, omapatrilat is considered a vasopeptidase inhibitor (VPI), because it functions to an equal extent as both an NEP inhibitor and an ACE (angiotensin converting enzyme) inhibitor. ACE is the enzyme that is responsible for converting Ang-I to Ang-II, which is the major pro-hypertensive hormone of the renin-angiotensin system. By inhibiting both NEP and ACE, it was thought that the increase in Ang-II caused by NEP inhibition would be negated, resulting in a highly effective antihypertensive treatment. Clinical studies, however, showed that omapatrilat was associated with a severe incidence of angioedema (a known side effect of ACE inhibitors). Later research has indicated that this may be due to concomitant inhibition of aminopeptidase P (APP). ACE, APP and NEP all contribute to the breakdown of bradykinin, which is another anti-hypertensive peptide, and the over-accumulation of bradykinin resulting from simultaneous inhibition of three of its degradation pathways may be a strong factor leading to angioedema.

The combination of a PDE1 inhibitor with an NEP inhibitor has been disclosed for the treatment of female sexual dysfunction (see European application publication EP 1 097 719 B1). The combination of the non-selective inhibitor vinpocetine (which also inhibits I-kappaB kinase) with an NEP inhibitor has been disclosed for treatment of serine protease-associated diseases, e.g., cardiac hypertrophy, hypertension, etc. (see WO 2013/039985). The combination of certain NEP inhibitors with phosphodiesterase inhibitors generally, and PDE5 inhibitors particularly, has been disclosed for the treatment of certain diseases including hypertension and heart failure (see U.S. Pat. No. 8,513,244). The combination of PDE1 inhibitors with dual NEP/ACE inhibitors (VPI's, such as omapatrilat) has been disclosed for the treatment of pathologic cardiac remodeling and heart failure (See US Patent Application Publication 2011/0190373). The use of a selective PDE5 inhibitor with an NEP inhibitor has been disclosed for the treatment of male sexual dysfunction (see US Patent Application Publication 2006/0041014).

Recently, the combination use of NEP inhibitors with angiotensin-II receptor blockers (ARBs) has been suggested for the treatment of hypertension. LCZ696 is a combination product containing the ARB valsartan with the NEP inhibitor AHU-377. This is another effort to get around the angiotensin-II mediated blood pressure effects caused by NEP inhibition, and the combination is currently undergoing clinical trials.

SUMMARY OF THE INVENTION

The present invention relates to the use of a PDE1 inhibitor in combination with a NEP inhibitor for the treatment of cardiac diseases and disorders, including, e.g., hypertension, heart failure, post-myocardial infarction management, cardiac hypertrophy and Duchenne Muscular Dystrophy (DMD). In a preferred embodiment, either the PDE1 inhibitor or the NEP inhibitor is selective. In a more preferred embodiment, both the PDE1 inhibitor and the NEP inhibitor are selective. Without being bound by theory, it is believed that the PDE1 inhibitors described are involved in regulating cGMP/PKG involvement in cardiac hypertrophy. Previous studies have demonstrated that intracellular Ca²⁺/CaM-dependent signaling promotes maladaptive hypertrophic gene expression in cardiomyocytes through various effectors such as the protein phosphatase calcineurin, Ca²⁺/CaM-dependent kinase II (CaMKII). Without being bound by any theory, endogenous cGMP/PKG-dependent signaling may be able to negatively regulate cardiac hypertrophy, by suppressing Gq/11 activation and normalizing Ca²⁺ signaling. Ca²⁺/CaM, by activating PDE1, may decrease cGMP levels and PKG activity. In turn, this process may lead to potentiated cardiomyocyte hypertrophy. Additionally, up-regulation of PDE1 expression upon neurohormonal or biomechanical stress during cardiac hypertrophy may further enhance PDE1 activity and attenuates cGMP/PKG signaling. In addition, the natriuretic peptides, and in particular C-type natriuretic peptide (CNP), are known to also exert anti-hypertrophic effects in cardiac tissues. These effects exerted by the natriuretic peptides are exerted via a cGMP signaling cascade. Accordingly, without being bound by any theory, it is believed that inhibition of PDE1, for example, could reverse or prevent the attenuation of cGMP/PKG signaling that contributes to cardiomyocyte hypertrophy. Such reversal or prevention of the attenuation of cGMP signaling would concomitantly and synergistically increase the anti-hypertrophic effects of the natriuretic peptides. Therefore, administration of a PDE1 inhibitor as described herein in combination with an NEP inhibitor, could provide a potential means to regulate cardiac hypertrophy, and by extension provide a treatment for various cardiovascular diseases and disorders.

In another embodiment, without being bound by theory, it is believed that PDE1 inhibitors, through their regulation of cGMP signaling cascades in vascular smooth muscle cells (e.g., induction of cGMP-mediated vasodilation), in combination with the effects of circulating ANP, BMP and/or CMP on the same smooth muscle cells, potentiated by the effects of NEP inhibition, will synergistically improve blood pressure. In a further embodiment, it is systolic blood pressure in particular that is improved. In yet a further embodiment, blood pressure and pulse pressure are both improved.

Without being bound by theory, the combination of a PDE1 inhibitor with a selective NEP inhibitor (not a VPI) should realize the full positive effects of NEP inhibition (increased ANP, BNP and CNP half-life), further enhanced by the potentiation of the NP signaling cascades (mediated by cGMP) caused by PDE1 inhibition, without the negative effects of NEP inhibition that can lead to decreased efficacy.

Accordingly, in one embodiment, the invention provides a new method of treatment or prophylaxis of a cardiovascular disease or disorder comprising administering to a patient in need thereof, an effective amount of an inhibitor of phosphodiesterase type 1 (e.g., PDE1 inhibitor, e.g., a PDE1A, PDE1B or PDE1C inhibitor) and an inhibitor of neutral endopeptidase (NEP or Neprilysin), in free or pharmaceutically acceptable salt form.

In one embodiment, the cardiovascular disease or disorder may selected from the group consisting of: atherosclerosis, hypertension, heart failure, congestive heart failure, angina, essential hypertension, pulmonary hypertension, secondary pulmonary hypertension, pulmonary arterial hypertension, isolated systolic hypertension, hypertension associated with diabetes, hypertension associated with atherosclerosis, renovascular hypertension, myocardial infarction and post-myocardial infarction. In certain embodiments, the cardiovascular disease or disorder to be treated may also relate to impaired cGMP/PKG-dependent signaling.

In a further embodiment, the invention also provides a method for the treatment or prophylaxis of cardiovascular disease or disorder that is associated with a muscular dystrophy (e.g, Duchenne, Becker, limb-girdle, myotonic, and Emery-Dreifuss Muscular Dystrophy) comprising administering to a patient in need thereof an effective amount of the compound of a PDE1 inhibitor and an NEP inhibitor as described herein, each in free or pharmaceutically acceptable salt form. As noted above, DMD is caused by the absence of a functional dystrophin protein, which in turn leads to reduced expression and mis-localization of dystrophin-associated proteins; which can include neuronal nitric oxide (NO) synthase. Disruption of nNOS signaling may result in muscle fatigue and unopposed sympathetic vasoconstriction during exercise, thereby increasing contraction-induced damage in dystrophin-deficient muscles. Without being bound by theory, the loss of normal nNOS signaling during exercise may be central to the vascular dysfunction proposed to be an important pathogenic mechanism in DMD. It is contemplated that by inhibiting phosphodiesterase 1 (e.g. PDE1A, PDE1C) and neutral endopeptidase, the invention described herein may circumvent defective nNOS signaling in dystrophic skeletal and/or cardiac muscle; thereby potentially improving cardiac outcomes in DMD patients.

In a further embodiment, the present invention provides for the use of a PDE1 inhibitor in combination with a selective NEP inhibitor, each in free or pharmaceutically acceptable salt form, in the manufacture of a medicament for the treatment or prophylaxis of a cardiovascular disease or disorder. In a further embodiment, the present invention also provides for the use of a PDE1 inhibitor in combination with a selective NEP inhibitor, each in free or pharmaceutically acceptable salt form, for the treatment of a cardiovascular disease or disorder. In a further embodiment, the present invention provides a PDE1 inhibitor in combination with a selective NEP inhibitor for use in the treatment or prophylaxis of a cardiovascular disease or disorder. In a further embodiment, the aforementioned cardiovascular disease or disorder is selected from the group consisting of: atherosclerosis, hypertension, heart failure, congestive heart failure, angina, essential hypertension, pulmonary hypertension, secondary pulmonary hypertension, pulmonary arterial hypertension, isolated systolic hypertension, hypertension associated with diabetes, hypertension associated with atherosclerosis, renovascular hypertension, myocardial infarction and post-myocardial infarction; or is a cardiovascular disease or disorder that is associated with a muscular dystrophy (e.g, Duchenne, Becker, limb-girdle, myotonic, and Emery-Dreifuss Muscular Dystrophy).

In another aspect, the present invention also includes a PDE1 inhibitor of Formula I, II, III, IV, V, VI, VII, VIII, IX, X, or XI described hereinbelow in free or salt form, in combination with a selective NEP inhibitor. In a preferred embodiment, the PDE1 inhibitor is a selective PDE1 inhibitor. In another embodiment, the invention further provides a pharmaceutical composition comprising a PDE1 inhibitor in combination with an NEP inhibitor, each in free or pharmaceutically acceptable salt form, in admixture with a pharmaceutically acceptable carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows PDE1 inhibition assay results for the compound of Example 20 of U.S. Pat. No. 8,273,750, obtained using the cellular screening assay method described herein with human cardiomyocytes.

FIG. 2 shows comparative PDE1 inhibition assay results for the compound of Example 20 of U.S. Pat. No. 8,273,750, obtained using the cellular screening assay method described herein with an HL60 macrophage cell line. The results compare the PDE1 inhibitory activity of various combinations of Example 20, ANP, ionomycin (a calcium ionophore) and SCH 51866 (a dual PDE1/PDE5 inhibitor).

FIG. 3 shows comparative PDE1 inhibition assay results for the compound of Example 20 of U.S. Pat. No. 8,273,750, obtained using the cellular screening assay method described herein with human cardiomyocytes, compared to the PDE5 inhibitors Sildenafil and Tadalafil.

DETAILED DESCRIPTION OF THE INVENTION

Compounds for Use in the Methods of the Invention

In one embodiment, the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are selective PDE1 inhibitors.

In another embodiment, the NEP inhibitors for use in the methods of treatment and prophylaxis described herein are selective NEP inhibitors.

PDE1 Inhibitors

In another embodiment, the PDE1 inhibitors are optionally substituted 4,5,7,8-tetrahydro-2H-imidazo[1,2-a]pyrrolo[3,4-e]pyrimidine or 4,5,7,8,9-pentahydro-2H-pyrimido[1,2-a]pyrrolo[3,4-e]pyrimidine, e.g., a Compound of Formula II, e.g., II-A or II-B:

wherein

-   -   (i) Q is C(═O), C(═S), C(═N(R₂₀)) or CH₂;     -   (ii) L is a single bond, —N(H)—, —CH₂—, —S—, —S(O)— or —S(O₂)—;     -   (iii) R₁ is H or C₁₋₄ alkyl (e.g., methyl);     -   (iv) R₄ is H or C₁₋₆ alkyl (e.g., methyl or isopropyl) and R₂         and R₃ are, independently,         -   H         -   C₁₋₆alkyl (e.g., methyl, isopropyl) optionally substituted             with halo or hydroxy (e.g., R₂ and R₃ are both methyl, or R₂             is H and R₃ is methyl, ethyl, isopropyl or hydroxyethyl),         -   aryl,         -   heteroaryl,         -   (optionally hetero)arylalkoxy,         -   (optionally hetero)arylC₁₋₆alkyl; or         -   R₂ and R₃ together form a 3- to 6-membered ring;         -   or         -   R₂ is H and R₃ and R₄ together form a di-, tri- or             tetramethylene bridge (pref. wherein the R₃ and R₄ together             have the cis configuration, e.g., where the carbons carrying             R₃ and R₄ have the R and S configurations, respectively);         -   or     -   (v) R₅ is         -   a) -D-E-F, wherein:             -   D is C₁₋₄alkylene (e.g., methylene, ethylene or                 prop-2-yn-1-ylene);             -   E is a single bond, C₂₋₄alkynylene (e.g., —C≡C—),                 arylene (e.g., phenylene) or heteroarylene (e.g.,                 pyridylene);             -   F is                 -   H,                 -   aryl (e.g., phenyl),                 -   heteroaryl (e.g., pyridyl, diazolyl, triazolyl, for                     example, pyrid-2-yl, imidazol-1-yl,                     1,2,4-triazol-1-yl), halo (e.g., F, Br, Cl),                 -   haloC₁₋₄alkyl (e.g., trifluoromethyl),                 -   —C(O)—R₁₅,                 -   —N(R₁₆)(R₁₇), or                 -   C₃₋₇cycloalkyl optionally containing at least one                     atom selected from a group consisting of N or O                     (e.g., cyclopentyl, cyclohexyl, pyrrolidinyl (e.g.,                     pyrrolidin-3-yl), tetrahydro-2H-pyran-4-yl, or                     morpholinyl);             -   wherein D, E and F are independently and optionally                 substituted with one or more halo (e.g., F, Cl or Br),                 C₁₋₄alkyl (e.g., methyl), haloC₁₋₄alkyl (e.g.,                 trifluoromethyl), C₁₋₄alkoxy (e.g., methoxy), hydroxy,                 C₁₋₄carboxy, or an additional aryl or heteroaryl (e.g.,                 biphenyl or pyridylphenyl),             -   for example, F is heteroaryl, e.g., pyridyl substituted                 with one or more halo (e.g., 6-fluoropyrid-2-yl,                 5-fluoropyrid-2-yl, 6-fluoropyrid-2-yl,                 3-fluoropyrid-2-yl, 4-fluoropyrid-2-yl,                 4,6-dichloropyrid-2-yl), haloC₁₋₄alkyl (e.g.,                 5-trifluoromethylpyrid-2-yl) or C₁₋₄alkyl (e.g.,                 5-methylpyrid-2-yl), or F is aryl, e.g., phenyl,                 substituted with one or more halo (e.g., 4-fluorophenyl)                 or F is a C₃₋₇heterocycloalkyl (e.g., pyrrolidinyl)                 optionally substituted with a C₁₋₆alkyl (e.g.,                 1-methylpyrrolidin-3-yl); or         -   b) a substituted heteroarylalkyl, e.g., substituted with             haloC₁₋₄alkyl;         -   c) attached to the nitrogen on the pyrrolo portion of             Formula II-A or II-B and is a moiety of Formula A

-   -   -   -   wherein X, Y and Z are, independently, N or C, and R₈,                 R₉, R₁₁ and R₁₂ are independently H or halogen (e.g., Cl                 or F), and R₁₀ is                 -   halogen,                 -   C₁₋₄alkyl,                 -   haloC₁₋₄alkyl (e.g., triflouromethyl)                 -   C₁₋₄alkoxy (e.g. methoxy),                 -   C₃₋₇cycloalkyl,                 -   heteroC₃₋₇cycloalkyl (e.g., pyrrolidinyl or                     piperidinyl),                 -   C₁₋₄haloalkyl (e.g., trifluoromethyl),                 -   aryl (e.g., phenyl),                 -   heteroaryl (e.g., pyridyl (for example pyrid-2-yl or                     pyrid-4-yl), or thiadiazolyl (e.g.,                     1,2,3-thiadiazol-4-yl)), diazolyl (e.g.,                     imidazol-1-yl), triazolyl (e.g.,                     1,2,4-triazol-1-yl), tetrazolyl,                 -   arylcarbonyl (e.g., benzoyl),                 -   alkylsulfonyl (e.g., methylsulfonyl),                 -   heteroarylcarbonyl, or                 -   alkoxycarbonyl;             -   wherein the aryl, heteroaryl, cycloalkyl or                 heterocycloalkyl is independently, optionally                 substituted with one or more C₁₋₄alkyl (e.g., methyl),                 halogen (e.g., chloro or fluoro), haloC₁₋₄alkyl (e.g.,                 trifluoromethyl), hydroxy, C₁₋₄carboxy, —SH or an                 additional aryl, heteroaryl (e.g., biphenyl or                 pyridylphenyl) or C₃₋₈cycloalkyl,             -   preferably R₁₀ is phenyl, pyridyl, piperidinyl or                 pyrrolidinyl optionally substituted with the                 substituents previously defined, e.g. optionally                 substituted with halo or alkyl             -   provided that when X, Y, or Z is nitrogen, R₈, R₉, or                 R₁₀, respectively, is not present;

    -   (vi) R₆ is         -   H,         -   C₁₋₄alkyl (e.g., methyl, ethyl, n-propyl, isobutyl),         -   C₃₋₇cycloalkyl (e.g., cyclopentyl or cyclohexyl),         -   heteroC₃₋₇cycloalkyl (e.g., pyrrolidinyl, piperidinyl,             morpholinyl),         -   aryl (e.g., phenyl),         -   heteroaryl (e.g., pyrid-4-yl),         -   arylC₁₋₄alkyl (e.g., benzyl),         -   arylamino (e.g., phenylamino),         -   heteroarylamino,         -   N,N-diC₁₋₄alkylamino,         -   N,N-diarylamino,         -   N-aryl-N-(arylC₁₋₄alkyl)amino (e.g.,             N-phenyl-N-(1,1′-biphen-4-ylmethyl)amino), or         -   N(R₁₈)(R₁₉),         -   wherein the aryl and heteroaryl are optionally substituted             with one or more C₁₋₄alkyl (e.g., methyl), halogen (e.g.,             chloro or fluoro), haloC₁₋₄alkyl (e.g., trifluoromethyl),             hydroxy, C₁₋₄carboxy, or an additional aryl, heteroaryl             (e.g., biphenyl or pyridylphenyl) or C₃₋₈cycloalkyl;

    -   (vii) R₇ is H, C₁₋₆alkyl (e.g., methyl or ethyl), halogen (e.g.,         Cl), —N(R₁₈)(R₁₉), hydroxy or C₁₋₆alkoxy;

    -   (viii) n=0 or 1;

    -   (ix) when n=1, A is —C(R₁₃R₁₄)—, wherein R₁₃ and R₁₄, are,         independently, H or C₁₋₄alkyl, aryl, heteroaryl, (optionally         hetero)arylC₁₋₄alkoxy, (optionally hetero)arylC₁₋₄alkyl or R₁₄         can form a bridge with R₂ or R₄;

    -   (x) R₁₈ is C₁₋₄alkyl, haloC₁₋₄alkyl, —OH or —OC₁₋₄alkyl (e.g.,         —OCH₃)

    -   (xi) R₁₆ and R₁₇ are independently H or C₁₋₄alkyl;

    -   (xii) R₁₈ and R₁₉ are independently         -   H,         -   C₁₋₄alky (e.g., methyl, ethyl, n-propyl, isobutyl),         -   C₃₋₈cycloalky (e.g., cyclohexyl or cyclopenyl),         -   heteroC₃₋₈cycloalky (e.g., pyrrolidinyl, piperidinyl,             morpholinyl),         -   aryl (e.g., phenyl) or         -   heteroaryl (e.g., pyridyl),         -   wherein said aryl and heteroaryl are optionally substituted             with one or more             -   halo (e.g., fluorophenyl, e.g., 4-fluorophenyl),             -   hydroxy (e.g., hydroxyphenyl, e.g., 4-hydroxyphenyl or                 2-hydroxyphenyl),             -   C₁₋₄alkyl (e.g., methyl),             -   haloC₁₋₄alkyl (e.g., trifluoromethyl),             -   C₁₋₄carboxy, or             -   an additional aryl, heteroaryl (e.g., biphenyl or                 pyridylphenyl) or C₃₋₈cycloalkyl,

    -   (xiii) R₂₀ is H, C₁₋₄alkyl or C₃₋₇cycloalkyl;         in free or salt form.

In another embodiment, the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are Compound of Formula I, e.g. Formula I-A and I-B:

wherein

-   -   (i) Q is C(═O), C(═S), C(═N(R₂₀)) or CH₂;     -   (ii) L is a single bond, —N(H)—, —CH₂—, —S—, —S(O)— or —S(O₂)—;     -   (iii) R₁ is H or C₁₋₄ alkyl (e.g., methyl);     -   (iv) R₄ is H or C₁₋₆ alkyl (e.g., methyl or isopropyl) and R₂         and R₃ are, independently,         -   H or C₁₋₆alkyl (e.g., methyl, isopropyl) optionally             substituted with halo or hydroxy (e.g., R₂ and R₃ are both             methyl, or R₂ is H and R₃ is methyl, ethyl, isopropyl or             hydroxyethyl),         -   aryl,         -   heteroaryl,         -   (optionally hetero)arylalkoxy, or (optionally             hetero)arylC₁₋₆alkyl;     -   or         -   R₂ is H and R₃ and R₄ together form a di-, tri- or             tetramethylene bridge (pref. wherein the R₃ and R₄ together             have the cis configuration, e.g., where the carbons carrying             R₃ and R₄ have the R and S configurations, respectively);     -   (v) R₅ is         -   a) -D-E-F, wherein:             -   D is C₁₋₄alkylene (e.g., methylene, ethylene or                 prop-2-yn-1-ylene);             -   E is a single bond, C₂₋₄alkynylene (e.g., —C≡C—),                 arylene (e.g., phenylene) or heteroarylene (e.g.,                 pyridylene);             -   F is                 -   H,                 -   aryl (e.g., phenyl),                 -   heteroaryl (e.g., pyridyl, diazolyl, triazolyl, for                     example, pyrid-2-yl, imidazol-1-yl,                     1,2,4-triazol-1-yl),                 -   halo (e.g., F, Br, Cl),                 -   haloC₁₋₄alkyl (e.g., trifluoromethyl),                 -   —C(O)—R₁₅,                 -   —N(R₁₆)(R₁₇), or                 -   C₃₋₇cycloalkyl optionally containing at least one                     atom selected from a group consisting of N or O                     (e.g., cyclopentyl, cyclohexyl, pyrrolidinyl (e.g.,                     pyrrolidin-3-yl), tetrahydro-2H-pyran-4-yl, or                     morpholinyl);             -   wherein D, E and F are independently and optionally                 substituted with one or more halo (e.g., F, Cl or Br),                 C₁₋₄alkyl (e.g., methyl), haloC₁₋₄alkyl (e.g.,                 trifluoromethyl), for example, F is heteroaryl, e.g.,                 pyridyl substituted with one or more halo (e.g.,                 6-fluoropyrid-2-yl, 5-fluoropyrid-2-yl,                 6-fluoropyrid-2-yl, 3-fluoropyrid-2-yl,                 4-fluoropyrid-2-yl, 4,6-dichloropyrid-2-yl),                 haloC₁₋₄alkyl (e.g., 5-trifluoromethylpyrid-2-yl) or                 C₁₋₄alkyl (e.g., 5-methylpyrid-2-yl), or F is aryl,                 e.g., phenyl, substituted with one or more halo (e.g.,                 4-fluorophenyl) or F is a C₃₋₇ heterocycloalkyl (e.g.,                 pyrrolidinyl) optionally substituted with a C₁₋₆alkyl                 (e.g., 1-methylpyrrolidin-3-yl); or         -   b) a substituted heteroarylalkyl, e.g., substituted with             haloalkyl;         -   c) attached to the nitrogen on the pyrrolo portion of             Formula I-A or I-B and is a moiety of Formula A

-   -   -   -   wherein X, Y and Z are, independently, N or C, and R₈,                 R₉, R₁₁ and R₁₂ are independently H or halogen (e.g., Cl                 or F), and R₁₀ is                 -   halogen,                 -   C₁₋₄alkyl,                 -   C₃₋₇cycloalkyl,                 -   C₁₋₄haloalkyl (e.g., trifluoromethyl),                 -   aryl (e.g., phenyl),                 -   heteroaryl (e.g., pyridyl (for example pyrid-2-yl),                     or thiadiazolyl (e.g., 1,2,3-thiadiazol-4-yl)),                     diazolyl, triazolyl, tetrazolyl,                 -   arylcarbonyl (e.g., benzoyl),                 -   alkylsulfonyl (e.g., methylsulfonyl),                 -   heteroarylcarbonyl, or                 -   alkoxycarbonyl;             -   provided that when X, Y, or Z is nitrogen, R₈, R₉, or                 R₁₀, respectively, is not present;

    -   (vi) R₆ is         -   H,         -   C₁₋₄alkyl,         -   C₃₋₇cycloalkyl (e.g., cyclopentyl),         -   aryl (e.g., phenyl),         -   heteroaryl (e.g., pyrid-4-yl),         -   arylC₁₋₄alkyl (e.g., benzyl),         -   arylamino (e.g., phenylamino),         -   heteroarylamino,         -   N,N-diC₁₋₄alkylamino,         -   N,N-diarylamino,         -   N-aryl-N-(arylC₁₋₄alkyl)amino (e.g.,             N-phenyl-N-(1,1′-biphen-4-ylmethyl)amino), or         -   —N(R₁₈)(R₁₉);         -   wherein the aryl or heteroaryl is optionally substituted             with one or more halo (e.g., F, Cl), hydroxy or C₁₋₆alkoxy;

    -   (vii) R₇ is H, C₁₋₆alkyl, halogen (e.g., Cl), —N(R₁₈)(R₁₉);

    -   (viii) n=0 or 1;

    -   (ix) when n=1, A is —C(R₁₃R₁₄)—, wherein R₁₃ and R₁₄, are,         independently, H or C₁₋₄alkyl, aryl, heteroaryl, (optionally         hetero)arylC₁₋₄alkoxy or (optionally hetero)arylC₁₋₄alkyl;

    -   (x) R₁₅ is C₁₋₄alkyl, haloC₁₋₄alkyl, —OH or —OC₁₋₄alkyl (e.g.,         —OCH₃)

    -   (xi) R₁₆ and R₁₇ are independently H or C₁₋₄alkyl;

    -   (xii) R₁₈ and R₁₉ are independently H, C₁₋₄alky or aryl (e.g.,         phenyl) wherein said aryl is optionally substituted with one or         more halo (e.g., fluorophenyl, e.g., 4-fluorophenyl) or hydroxy         (e.g., hydroxyphenyl, e.g., 4-hydroxyphenyl or 2-hydroxyphenyl)

    -   (xiii) R₂₀ is H, C₁₋₄alkyl or C₃₋₇cycloalkyl;         in free or salt form.

    -   1.1 any of the preceding formulae wherein the compounds inhibit         phosphodiesterase-mediated (e.g., PDE1-mediated, especially         PDE1B-mediated) hydrolysis of cGMP, e.g., with an IC₅₀ of less         than 1 μM, preferably less than 750 nM, more preferably less         than 500 nM, more preferably less than 50 nM in an         immobilized-metal affinity particle reagent PDE assay,

in free or salt form.

The invention further provides optionally substituted 4,5,7,8-tetrahydro-(optionally 4-thioxo or 4-imino)-(1H or 2H)-imidazo[1,2-a]pyrazolo[4,3-e]pyrimidine or 4,5,7,8,9-pentahydro-(1H or 2H)-pyrimido[1,2-a]pyrazolo[4,3-e]pyrimidine compounds, in free or salt form, e.g., (1 or 2 and/or 3 and/or 5)-substituted 4,5,7,8-tetrahydro-1H-imidazo[1,2-a]pyrazolo[4,3-e]pyrimidine, 4,5,7,8-tetrahydro-2H-imidazo[1,2-a]pyrazolo[4,3-e]pyrimidine, 4,5,7,8-tetrahydro-(1H or 2H)-pyrimido[1,2-a]pyrazolo[4,3-e]pyrimidine-4(5H)-imine, 7,8-dihydro-1H-imidazo[1,2-a]pyrazolo[4,3-e]pyrimidine-4(5H)-thione or 7,8-dihydro-2H-imidazo[1,2-a]pyrazolo[4,3-e]pyrimidine-4(5H)-thione compounds, e.g., a Compound of Formula III:

wherein

-   -   (i) Q is C(═S), C(═N(R₂₀)) or CH₂;     -   (ii) L is a single bond, —N(H)—, —CH₂—;     -   (iii) R₁ is H or C₁₋₄ alkyl (e.g., methyl or ethyl);     -   (iv) R₄ is H or C₁₋₆ alkyl (e.g., methyl, isopropyl) and R₂ and         R₃ are, independently:         -   H or C₁₋₆alkyl (e.g., methyl or isopropyl) optionally             substituted with halo or hydroxy (e.g., R₂ and R₃ are both             methyl, or R₂ is H and R₃ is methyl, ethyl, isopropyl or             hydroxyethyl), aryl,         -   heteroaryl,         -   (optionally hetero)arylalkoxy,         -   (optionally hetero)arylC₁₋₆alkyl, or         -   R₂ and R₃ together form a 3- to 6-membered ring;         -   or         -   R₂ is H and R₃ and R₄ together form a di-, tri- or             tetramethylene bridge (pref. wherein the R₃ and R₄ together             have the cis configuration, e.g., where the carbons carrying             R₃ and R₄ have the R and S configurations, respectively);     -   (v) R₅ is         -   d) -D-E-F, wherein:             -   D is C₁₋₄alkylene (e.g., methylene, ethylene or                 prop-2-yn-1-ylene);             -   E is a single bond, C₂₋₄alkynylene (e.g., —C≡C—),                 arylene (e.g., phenylene) or heteroarylene (e.g.,                 pyridylene);             -   F is                 -   H,                 -   aryl (e.g., phenyl),                 -   heteroaryl (e.g., pyridyl, diazolyl, triazolyl, for                     example, pyrid-2-yl, imidazol-1-yl,                     1,2,4-triazol-1-yl),                 -   halo (e.g., F, Br, Cl),                 -   haloC₁₋₄alkyl (e.g., trifluoromethyl),                 -   —C(O)—R₁₅,                 -   —N(R₁₆)(R₁₇),                 -   —S(O)₂R₂₁ or                 -   C₃₋₇cycloalkyl optionally containing at least one                     atom selected from a group consisting of N or O                     (e.g., cyclopentyl, cyclohexyl, pyrrolidinyl (e.g.,                     pyrrolidin-3-yl), tetrahydro-2H-pyran-4-yl, or                     morpholinyl);             -   wherein D, E and F are independently and optionally                 substituted with one or more:                 -   halo (e.g., F, Cl or Br),                 -   C₁₋₄alkyl (e.g., methyl),                 -   haloC₁₋₄alkyl (e.g., trifluoromethyl),                 -   C₁₋₄alkoxy) or                 -   C₁₋₄alkyl (e.g., 5-methylpyrid-2-yl),             -   for example, F is heteroaryl, e.g., pyridyl substituted                 with one or more halo (e.g., 6-fluoropyrid-2-yl,                 5-fluoropyrid-2-yl, 6-fluoropyrid-2-yl,                 3-fluoropyrid-2-yl, 4-fluoropyrid-2-yl,                 4,6-dichloropyrid-2-yl),             -   or F is aryl, e.g., phenyl, substituted with one or more                 halo (e.g., 4-fluorophenyl)             -   or F is a C₃₋₇heterocycloalkyl (e.g., pyrrolidinyl)                 optionally substituted with a C₁₋₆alkyl (e.g.,                 1-methylpyrrolidin-3-yl);             -   or         -   e) a substituted heteroarylalkyl, e.g., substituted with             haloalkyl;         -   f) attached to one of the nitrogens on the pyrazolo portion             of Formula III and is a moiety of Formula A

-   -   -   -   wherein X, Y and Z are, independently, N or C, and R₈,                 R₉, R₁₁ and R₁₂ are independently H or halogen (e.g., Cl                 or F), and R₁₀ is:                 -   halogen,                 -   C₁₋₄alkyl,                 -   C₃₋₇cycloalkyl,                 -   hetC₃₋₇cycloalkyl (e.g., pyrrolidinyl or                     piperidinyl),                 -   C₁₋₄haloalkyl (e.g., trifluoromethyl),                 -   aryl (e.g., phenyl),                 -   heteroaryl (e.g., pyridyl (for example pyrid-2-yl),                     or thiadiazolyl (e.g., 1,2,3-thiadiazol-4-yl)),                     diazolyl, triazolyl, tetrazolyl,                 -   arylcarbonyl (e.g., benzoyl),                 -   alkylsulfonyl (e.g., methylsulfonyl),                 -   heteroarylcarbonyl, or                 -   alkoxycarbonyl;             -   wherein the aryl, heteroaryl, cycloalkyl or                 heterocycloalkyl is independently and optionally                 substituted with one or more halo (e.g., F or Cl),                 C₁₋₄alkyl, C₁₋₄alkoxy, C₁₋₄haloalkyl (e.g.,                 trifluoromethyl), —SH;             -   preferably R₁₀ is phenyl, pyridyl, piperidinyl or                 pyrrolidinyl optionally substituted with the                 substituents previously defined, e.g. optionally                 substituted with halo or alkyl             -   provided that when X, Y, or Z is nitrogen, R₈, R₉, or                 R₁₀, respectively, is not present;

    -   (vi) R₆ is         -   H,         -   C₁₋₄alkyl,         -   C₃₋₇cycloalkyl (e.g., cyclopentyl),         -   aryl (e.g., phenyl),         -   heteroaryl (e.g., pyridyl, for example, pyrid-4-yl),         -   arylC₁₋₄alkyl (e.g., benzyl),         -   arylamino (e.g., phenylamino),         -   heterarylamino,         -   N,N-diC₁₋₄alkylamino,         -   N,N-diarylamino,         -   N-aryl-N-(arylC₁₋₄alkyl)amino (e.g.,             N-phenyl-N-(1,1′-biphen-4-ylmethyl)amino), or         -   —N(R₁₈)(R₁₉);         -   wherein the aryl or heteroaryl is optionally substituted             with one or more halo (e.g., F, Cl), hydroxy, C₁₋₆alkyl,             C₁₋₆alkoxy, C₃₋₈cycloalkyl, for example, R₆ is             4-hydroxyphenyl or 4-fluorophenyl,

    -   (vii) n=0 or 1;

    -   (viii) when n=1, A is —C(R₁₃R₁₄)—, wherein R₁₃ and R₁₄, are,         independently, H or C₁₋₄alkyl, aryl, heteroaryl, (optionally         hetero)arylC₁₋₄alkoxy, (optionally hetero)arylC₁₋₄alkyl or R₁₃         or R₁₄ can form a bridge with R₂ or R₄;

    -   (ix) R₁₅ is C₁₋₄alkyl, haloC₁₋₄alkyl, —OH or —OC₁₋₄alkyl (e.g.,         —OCH₃)

    -   (x) R₁₆ and R₁₇ are independently H or C₁₋₄alkyl;

    -   (xi) R₁₈ and R₁₉ are independently         -   H,         -   C₁₋₄alky,         -   C₃₋₈cycloalkyl,         -   heteroC₃₋₈cycloalkyl,         -   aryl (e.g., phenyl), or         -   heteroaryl,         -   wherein said aryl or heteroaryl is optionally substituted             with one or more             -   halo (e.g., fluorophenyl, e.g., 4-fluorophenyl),             -   hydroxy (e.g., hydroxyphenyl, e.g., 4-hydroxyphenyl or                 2-hydroxyphenyl),             -   C₁₋₆alkyl,             -   haloC₁₋₆alkyl,             -   C₁₋₆alkoxy,             -   aryl,             -   heteroaryl, or             -   C₃₋₈cycloalkyl;

    -   (xii) R₂₀ is H, C₁₋₄alkyl (e.g., methyl) or C₃₋₇cycloalkyl,

    -   (xiii) R₂₁ is C₁₋₆alkyl;         in free or salt form.

In yet another embodiment, the invention also provides a Compound of Formula

wherein

-   -   (i) Q is C(═S), C(═N(R₂₀)) or CH₂;     -   (ii) L is a single bond, —N(H)—, —CH₂—;     -   (iii) R₁ is H or C₁₋₄ alkyl (e.g., methyl or ethyl);     -   (iv) R₄ is H or C₁₋₆ alkyl (e.g., methyl, isopropyl) and R₂ and         R₃ are, independently, H or C₁₋₆alkyl (e.g., methyl or         isopropyl) optionally substituted with halo or hydroxy (e.g., R₂         and R₃ are both methyl, or R₂ is H and R₃ is methyl, ethyl,         isopropyl or hydroxyethyl), aryl, heteroaryl, (optionally         hetero)arylalkoxy, or (optionally hetero)arylC₁₋₆alkyl; or         -   R₂ is H and R₃ and R₄ together form a di-, tri- or             tetramethylene bridge (pref. wherein the R₃ and R₄ together             have the cis configuration, e.g., where the carbons carrying             R₃ and R₄ have the R and S configurations, respectively);     -   (v) R₅ is         -   a) -D-E-F, wherein:             -   D is C₁₋₄alkylene (e.g., methylene, ethylene or                 prop-2-yn-1-ylene);             -   E is a single bond, C₂₋₄alkynylene (e.g., —C≡C—),                 arylene (e.g., phenylene) or heteroarylene (e.g.,                 pyridylene);             -   F is H, aryl (e.g., phenyl), heteroaryl (e.g., pyridyl,                 diazolyl, triazolyl, for example, pyrid-2-yl,                 imidazol-1-yl, 1,2,4-triazol-1-yl), halo (e.g., F, Br,                 Cl), haloC₁₋₄alkyl (e.g., trifluoromethyl), —C(O)—R₁₅,                 —N(R₁₆)(R₁₇), —S(O)₂R₂₁ or C₃₋₇cycloalkyl optionally                 containing at least one atom selected from a group                 consisting of N or O (e.g., cyclopentyl, cyclohexyl,                 pyrrolidinyl (e.g., pyrrolidin-3-yl),                 tetrahydro-2H-pyran-4-yl, or morpholinyl);             -   wherein D, E and F are independently and optionally                 substituted with one or more:                 -   halo (e.g., F, Cl or Br),                 -   C₁₋₄alkyl (e.g., methyl),             -   haloC₁₋₄alkyl (e.g., trifluoromethyl),             -   for example, F is heteroaryl, e.g., pyridyl substituted                 with one or more halo (e.g., 6-fluoropyrid-2-yl,                 5-fluoropyrid-2-yl, 6-fluoropyrid-2-yl,                 3-fluoropyrid-2-yl, 4-fluoropyrid-2-yl,                 4,6-dichloropyrid-2-yl), haloC₁₋₄alkyl (e.g.,                 5-trifluoromethylpyrid-2-yl) or C₁₋₄alkyl (e.g.,                 5-methylpyrid-2-yl),             -   or F is aryl, e.g., phenyl, substituted with one or more                 halo (e.g., 4-fluorophenyl)             -   or F is a C₃₋₇heterocycloalkyl (e.g., pyrrolidinyl)                 optionally substituted with a C₁₋₆alkyl (e.g.,                 1-methylpyrrolidin-3-yl);             -   or         -   b) a substituted heteroarylalkyl, e.g., substituted with             haloalkyl;         -   c) attached to one of the nitrogens on the pyrazolo portion             of Formula IV and is a moiety of Formula A

-   -   -   -   wherein X, Y and Z are, independently, N or C, and R₈,                 R₉, R₁₁ and R₁₂ are independently H or halogen (e.g., Cl                 or F), and R₁₀ is:                 -   halogen,                 -   C₁₋₄alkyl,                 -   C₃₋₇cycloalkyl,                 -   C₁₋₄haloalkyl (e.g., trifluoromethyl),                 -   aryl (e.g., phenyl),                 -   heteroaryl (e.g., pyridyl (for example pyrid-2-yl),                     or                 -   thiadiazolyl (e.g., 1,2,3-thiadiazol-4-yl)),                     diazolyl, triazolyl, tetrazolyl,                 -   arylcarbonyl (e.g., benzoyl),                 -   alkylsulfonyl (e.g., methylsulfonyl),                 -   heteroarylcarbonyl, or alkoxycarbonyl;             -   provided that when X, Y, or Z is nitrogen, R₈, R₉, or                 R₁₀, respectively, is not present;

    -   (vi) R₆ is         -   H,         -   C₁₋₄alkyl,         -   C₃₋₇cycloalkyl (e.g., cyclopentyl),         -   aryl (e.g., phenyl),         -   heteroaryl (e.g., pyridyl, for example, pyrid-4-yl),         -   arylC₁₋₄alkyl (e.g., benzyl),         -   arylamino (e.g., phenylamino),         -   heterarylamino,         -   N,N-diC₁₋₄alkylamino,         -   N,N-diarylamino,         -   N-aryl-N-(arylC₁₋₄alkyl)amino (e.g.,             N-phenyl-N-(1,1′-biphen-4-ylmethyl)amino), or         -   —N(R₁₈)(R₁₉);         -   wherein the aryl or heteroaryl is optionally substituted             with one or more halo (e.g., F, Cl), hydroxy or C₁₋₆alkoxy,             for example, R₆ is 4-hydroxyphenyl or 4-fluorophenyl,

    -   (vii) n=0 or 1;

    -   (viii) when n=1, A is —C(R₁₃R₁₄)—, wherein R₁₃ and R₁₄, are,         independently, H or C₁₋₄alkyl, aryl, heteroaryl, (optionally         hetero)arylC₁₋₄alkoxy or (optionally hetero)arylC₁₋₄alkyl;

    -   (ix) R₁₅ is C₁₋₄alkyl, haloC₁₋₄alkyl, —OH or —OC₁₋₄alkyl (e.g.,         —OCH₃)

    -   (x) R₁₆ and R₁₇ are independently H or C₁₋₄alkyl;

    -   (xi) R₁₈ and R₁₉ are independently H, C₁₋₄alky or aryl (e.g.,         phenyl) wherein said aryl is optionally substituted with one or         more halo (e.g., fluorophenyl, e.g., 4-fluorophenyl) or hydroxy         (e.g., hydroxyphenyl, e.g., 4-hydroxyphenyl or 2-hydroxyphenyl)

    -   (xii) R₂₀ is H, C₁₋₄alkyl (e.g., methyl) or C₃₋₇cycloalkyl,

    -   (xiii) R₂₁ is C₁₋₆alkyl;         in free or salt form.

In still yet another embodiment, the invention provides that the PDE1 inhibitors for use in the methods of treatment and prophylaxis which are described herein are selected from any of the following: US 2008-0188492 A1, US 2010-0173878 A1, US 2010-0273754 A1, US 2010-0273753 A1, WO 2010/065153, WO 2010/065151, WO 2010/065151, WO 2010/065149, WO 2010/065147, WO 2010/065152, WO 2011/153129, WO 2011/133224, WO 2011/153135, WO 2011/153136, and WO 2011/153138, the contents of each of which are incorporated herein by reference in their entireties.

In yet another embodiment the invention provides that the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are compounds of Formula V:

wherein

-   -   (i) R₁ is H or C₁₋₄ alkyl (e.g., methyl);     -   (ii) R₄ is H or C₁₋₄ alkyl and R₂ and R₃ are, independently, H         or C₁₋₄ alkyl (e.g., R₂ and R₃ are both methyl, or R₂ is H and         R₃ is isopropyl), aryl, heteroaryl, (optionally         hetero)arylalkoxy, or (optionally hetero)arylalkyl;     -   or     -   R₂ is H and R₃ and R₄ together form a di-, tri- or         tetramethylene bridge (pref. wherein the R₃ and R₄ together have         the cis configuration, e.g., where the carbons carrying R₃ and         R₄ have the R and S configurations, respectively);     -   (iii) R₅ is a substituted heteroarylalkyl, e.g., substituted         with haloalkyl or     -   R₅ is attached to one of the nitrogens on the pyrazolo portion         of Formula V and is a moiety of Formula A

wherein X, Y and Z are, independently, N or C, and R₈, R₉, R₁₁ and R₁₂ are independently H or halogen (e.g., Cl or F), and R₁₀ is halogen, alkyl, cycloalkyl, haloalkyl (e.g., trifluoromethyl), aryl (e.g., phenyl), heteroaryl (e.g., pyridyl (for example pyrid-2-yl), or thiadiazolyl (e.g., 1,2,3-thiadiazol-4-yl)), diazolyl, triazolyl, tetrazolyl, arylcarbonyl (e.g., benzoyl), alkylsulfonyl (e.g., methylsulfonyl), heteroarylcarbonyl, or alkoxycarbonyl; provided that when X, Y, or Z is nitrogen, R₈, R₉, or R₁₀, respectively, is not present; and

-   -   (iv) R₆ is H, alkyl, aryl, heteroaryl, arylalkyl (e.g., benzyl),         arylamino (e.g., phenylamino), heterarylamino, N,N-dialkylamino,         N,N-diarylamino, or N-aryl-N-(arylakyl)amino (e.g.,         N-phenyl-N-(1,1′-biphen-4-ylmethyl)amino); and     -   (v) n=0 or 1;     -   (vi) when n=1, A is —C(R₁₃R₁₄)—         -   wherein R₁₃ and R₁₄, are, independently, H or C₁₋₄ alkyl,             aryl, heteroaryl, (optionally hetero)arylalkoxy or             (optionally hetero)arylalkyl;             in free, salt or prodrug form, including its enantiomers,             diastereoisomers and racemates.

In one embodiment the invention provides that the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are compounds of Formula VI:

wherein:

-   -   (i) R₁ is H or alkyl;     -   (ii) R₂ is H, alkyl, cycloalkyl, haloalkyl, alkylaminoalkyl,         hydroxyalkyl, arylalkyl, heteroarylalkyl, or alkoxyarylalkyl;     -   (iii) R₃ is heteroarylmethyl or formula A

wherein X, Y and Z are, independently, N or C, and R₈, R₉, R₁₁ and R₁₂ are independently H or halogen; and R₁₀ is halogen, alkyl, cycloalkyl, haloalkyl, aryl, heteroaryl, alkyl sulfonyl, arylcarbonyl, heteroarylcarbonyl, alkoxycarbonyl, or aminocarbonyl;

-   -   (iv) R₄ is aryl or heteroaryl; and     -   (v) R₅ is H, alkyl, cycloalkyl, heteroaryl, aryl, p-benzylaryl;         provided that when X, Y or X is nitrogen, R₈, R₉ or R₁₀,         respectively, is not present; wherein “alk” or “alkyl” refers to         C₁₋₆ alkyl and “cycloalkyl” refers to C₃₋₆ cycloalkyl, in free,         salt or physiologically hydrolysable and acceptable ester         prodrug form.

In one embodiment the invention provides that the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are compounds of Formula VII:

(i) X is C₁₋₆alkylene (e.g., methylene, ethylene or prop-2-yn-1-ylene); (ii) Y is a single bond, alkynylene (e.g., —C≡C—), arylene (e.g., phenylene) or heteroarylene (e.g., pyridylene); (iii) Z is H, aryl (e.g., phenyl), heteroaryl (e.g., pyridyl, e.g., pyrid-2-yl), halo (e.g., F, Br, Cl), haloC₁₋₆alkyl (e.g., trifluoromethyl), —C(O)—R, —N(R²)(R³), or C₃₋₇cycloalkyl optionally containing at least one atom selected from a group consisting of N or O (e.g., cyclopentyl, cyclohexyl, tetrahydro-2H-pyran-4-yl, or morpholinyl); (iv) R¹ is C₁₋₆alkyl, haloC₁₋₆alkyl, —OH or —OC₁₋₆alkyl (e.g., —OCH₃); (v) R² and R³ are independently H or C₁₋₆alkyl; (vi) R⁴ and R⁵ are independently H, C₁₋₆alky or aryl (e.g., phenyl) optionally substituted with one or more halo (e.g., fluorophenyl, e.g., 4-fluorophenyl), hydroxy (e.g., hydroxyphenyl, e.g., 4-hydroxyphenyl or 2-hydroxyphenyl) or C₁₋₆alkoxy; (vii) wherein X, Y and Z are independently and optionally substituted with one or more halo (e.g., F, Cl or Br), C₁₋₆alkyl (e.g., methyl), haloC₁₋₆alkyl (e.g., trifluoromethyl), for example, Z is heteroaryl, e.g., pyridyl substituted with one or more halo (e.g., 6-fluoropyrid-2-yl, 5-fluoropyrid-2-yl, 6-fluoropyrid-2-yl, 3-fluoropyrid-2-yl, 4-fluoropyrid-2-yl, 4,6-dichloropyrid-2-yl), haloC₁₋₆alkyl (e.g., 5-trifluoromethylpyrid-2-yl) or C₁₋₆-alkyl (e.g., 5-methylpyrid-2-yl), or Z is aryl, e.g., phenyl, substituted with one or more halo (e.g., 4-fluorophenyl), in free, salt or prodrug form.

In further embodiment, the invention provides that the PDE1 inhibitor of Formula VII is:

in free, salt (e.g., pharmaceutically acceptable salt) or prodrug form.

In one embodiment, the invention provides that the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are compounds of Formula VIII:

wherein

-   -   (i) R₁ is H or C₁₋₆alkyl;     -   (ii) R₂ is         -   H,         -   C₁₋₆alkyl,         -   C₃₋₈cycloalkyl optionally substituted with one or more             amino,         -   C₃₋₈heterocycloalkyl optionally substituted with C₁₋₆alkyl,         -   C₃₋₈cycloalkyl-C₁₋₆alkyl,         -   C₁₋₆haloalkyl,         -   C₀₋₆alkylaminoC₀₋₆alkyl,         -   hydroxyC₁₋₆alkyl,         -   arylC₀₋₆alkyl,         -   heteroarylalkyl,         -   C₁₋₆alkoxyarylC₁₋₆alkyl, or         -   -G-J wherein:             -   G is a single bond or, alkylene;             -   J is cycloalkyl or heterocycloalkyl optionally                 substituted with alkyl;     -   (iii) R₃ is         -   a) -D-E-F wherein             -   1. D is single bond, C₁₋₆alkylene or arylC₁₋₆alkylene;             -   2. E is a C₁₋₆alkylene, arylene, C₁₋₆alkylarylene,                 aminoC₁₋₆alkylene- or amino; and             -   3. F is heteroC₃₋₈cycloalkyl optionally substituted with                 C₁₋₆alkyl;     -   (iv) R₄ is aryl optionally substituted with one or more halo,         hydroxy or C₁₋₆alkoxy; heteroaryl; or heteroC₃₋₆cycloalkyl; and     -   (v) R₅ is H, C₁₋₆alkyl, C₃₋₈cycloalkyl, heteroaryl, aryl or         p-benzylaryl;         wherein “alk”, “alkyl”, “haloalkyl” or “alkoxy” refers to C₁₋₆         alkyl and “cycloalkyl” refers to C₃₋₈cycloalkyl;         in free or salt form.

In another embodiment the invention provides that the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are compounds of Formula IX:

wherein

-   -   (i) Q is —C(═S)—, —C(═N(R₆))— or —C(R₁₄)(R₁₅)—;     -   (ii) R₁ is H or C₁₋₆alkyl (e.g., methyl or ethyl);     -   (iii) R₂ is         -   H,         -   C₁₋₆alkyl (e.g., isopropyl, isobutyl, 2-methylbutyl or             2,2-dimethylpropyl) wherein said alkyl group is optionally             substituted with one or more halo (e.g., fluoro) or hydroxy             (e.g., hydroxyC₁₋₆alkyl, for example 1-hydroxyprop-2-yl or             3-hydroxy-2-methylpropyl),         -   haloC₁₋₆alkyl (e.g., trifluoromethyl or             2,2,2-trifluoroethyl), N(R₁₄)(R₁₅)—C₁₋₆alkyl (e.g.,             2-(dimethylamino)ethyl or 2-aminopropyl),         -   arylC₀₋₆alkyl (e.g., phenyl or benzyl), wherein said aryl is             optionally substituted with one or more C₁₋₆alkoxy, for             example, C₁₋₆alkoxyarylC₀₋₆alkyl (e.g., 4-methoxybenzyl),         -   heteroarylC₀₋₆alkyl (e.g., pyridinylmethyl), wherein said             heteroaryl is optionally substituted with one or more             C₁₋₆alkoxy (e.g., C₁₋₆alkoxyheteroarylC₁₋₆alkyl);         -   -G-J wherein G is a single bond or C₁₋₆alkylene (e.g.,             methylene) and J is C₃₋₈cycloalkyl or heteroC₃₋₈cycloalkyl             (e.g., oxetan-2-yl, pyrrolidin-3-yl, pyrrolidin-2-yl)             wherein the cycloalkyl and heterocycloalkyl group are             optionally substituted with one or more C₁₋₆alkyl or amino,             for example,             -   —C₀₋₄alkyl-C₃₋₈cycloalkyl (e.g., —C₀₋₄alkyl-cyclopentyl,                 —C₀₋₄alkyl-cyclohexyl or —C₀₋₄alkyl-cyclopropyl),                 wherein said cycloalkyl is optionally substituted with                 one or more C₁₋₆alkyl or amino (for example,                 2-aminocyclopentyl or 2-aminocyclohexyl),             -   —C₀₋₄alkyl-C₃₋₈heterocycloalkyl (e.g.,                 —C₀₋₄alkyl-pyrrolidinyl, for example,                 —C₀₋₄alkylpyrrolidin-3-yl) wherein said heterocycloalkyl                 is optionally substituted with C₁₋₆alkyl (e.g., methyl),                 for example, 1-methylpyrrolidin-3-yl,                 1-methyl-pyrrolindin-2-yl,                 1-methyl-pyrrolindin-2-yl-methyl or                 1-methyl-pyrrolindin-3-yl-methyl);     -   (iv) R₃ is         -   1) -D-E-F wherein:             -   D is a single bond, C₁₋₆alkylene (e.g., methylene), or                 arylC₁₋₆alkylene (e.g., benzylene or —CH₂C₆H₄—);             -   E is                 -   a single bond,                 -   C₁₋₄alkylene (e.g., methylene, ethynylene,                     prop-2-yn-1-ylene),                 -   C₀₋₄alkylarylene (e.g., phenylene or —C₆H₄—,                     -benzylene- or —CH₂C₆H₄—), wherein the arylene group                     is optionally substituted with halo (e.g., Cl or F),                 -   heteroarylene (e.g., pyridinylene or                     pyrimidinylene), aminoC₁₋₆alkylene (e.g.,                     —CH₂N(H)—), amino (e.g., —N(H)—);                 -   C₃₋₈cycloalkylene optionally containing one or more                     heteroatom selected from N or O (e.g.,                     piperidinylene),             -   F is                 -   H,                 -   halo (e.g., F, Br, Cl),                 -   C₁₋₆alkyl (e.g., isopropyl or isobutyl),                 -   haloC₁₋₆alkyl (e.g., trifluoromethyl), aryl (e.g.,                     phenyl),                 -   C₃₋₈cycloalkyl optionally containing one or more                     atom selected from a group consisting of N, S or O                     (e.g., cyclopentyl, cyclohexyl, piperidinyl,                     pyrrolidinyl, tetrahydro-2H-pyran-4-yl, or                     morpholinyl), and optionally substituted with one or                     more C₁₋₆alkyl (e.g., methyl or isopropyl), for                     example, 1-methylpyrrolidin-2-yl, pyrrolidin-1-yl,                     pyrrolidin-2-yl, piperidin-2-yl,                     1-methylpiperidin-2-yl, 1-ethylpiperidin-2-yl,                 -   heteroaryl (e.g., pyridyl (for example, pyrid-2-yl),                     pyrimidinyl (for example, pyrimidin-2-yl),                     thiadiazolyl (for example, 1,2,3-thiadiazol-4-yl),                     diazolyl (e.g., pyrazolyl (for example,                     pyrazol-1-yl) or imidazolyl (for example,                     imidazol-1-yl, 4-methylimidazolyl,                     1-methylimidazol-2-yl)), triazolyl (e.g.,                     1,2,4-triazol-1-yl), tetrazolyl (e.g.,                     tetrazol-5-yl), alkyloxadiazolyl (e.g.,                     5-methyl-1,2,4-oxadiazol), wherein said heteroaryl                     is optionally substituted with one or more                     C₁₋₆alkyl, halo (e.g., fluoro) or haloC₁₋₆alkyl;                 -   C₁₋₆alkoxy,                 -   —O-haloC₁₋₆alkyl (e.g., —O—CF₃),                 -   C₁₋₆alkylsulfonyl (for example, methylsulfonyl or                     —S(O)₂CH₃), —C(O)—R₁₃, wherein R₁₃ is —N(R₁₄)(R₁₅),                     C₁₋₆alkyl (e.g., methyl), —OC₁₋₆alkyl (e.g., —OCH₃),                     haloC₁₋₆alkyl (trifluoromethyl), aryl (e.g.,                     phenyl), or heteroaryl;                 -   —N(R₁₄)(R₁₅);             -   or         -   2) a substituted heteroarylC₁₋₆aklyl, e.g., substituted with             haloC₁₋₆alkyl;             -   or         -   3) attached to one of the nitrogens on the pyrazolo portion             of Formula I and is a moiety of Formula A

-   -   -   -   wherein:                 -   X, Y and Z are, independently, N or C,                 -   R₈, R₉, R₁₁ and R₁₂ are independently H or halogen                     (e.g., Cl or F); and                 -   R₁₀ is                 -    halogen (e.g., fluoro or chloro),                 -    C₁₋₆alkyl,                 -    C₃₋₈cycloalkyl,                 -    heteroC₃₋₈cycloalkyl (e.g., pyrrolidinyl or                     piperidinyl),                 -    haloC₁₋₆alkyl (e.g., trifluoromethyl), aryl (e.g.,                     phenyl) or heteroaryl (e.g., pyridyl, (for example,                     pyrid-2-yl) or e.g., thiadiazolyl (for example,                     1,2,3-thiadiazol-4-yl), diazolyl, triazolyl (e.g.,                     1,2,4-triazol-1-yl), tetrazolyl (e.g.,                     tetrazol-5-yl), alkyloxadiazolyl (e.g.,                     5-methyl-1,2,4-oxadiazol), pyrazolyl (e.g.,                     pyrazol-1-yl),                 -    wherein said aryl, heteroaryl, cycloalkyl or                     heterocycloalkyl is optionally substituted with one                     or more C₁₋₆alkyl (e.g., methyl), halogen (e.g.,                     chloro or fluoro), haloC₁₋₆alkyl (e.g.,                     trifluoromethyl), hydroxy, carboxy, —SH, or an                     additional aryl or heteroaryl (e.g., biphenyl or                     pyridylphenyl),                 -    C₁₋₆alkyl sulfonyl (e.g., methyl sulfonyl),                 -    arylcarbonyl (e.g., benzoyl),                 -    heteroarylcarbonyl,                 -    C₁₋₆alkoxycarbonyl, (e.g., methoxycarbonyl),                     Aminocarbonyl,                 -    —N(R₁₄)(R₁₅);                 -    preferably R₁₀ is phenyl, pyridyl, piperidinyl or                     pyrrolidinyl optionally substituted with the                     substituents previously defined, e.g. optionally                     substituted with halo or alkyl;                 -   provided that when X, Y or X is nitrogen, R₈, R₉ or                     R₁₀, respectively, is not present;

    -   (v) R₄ and R₅ are independently:         -   H,         -   C₁₋₆alkyl (e.g., methyl, isopropyl, isobutyl, n-propyl),         -   C₃₋₈cycloalkyl (e.g., cyclopentyl or cyclohexyl),         -   C₃₋₈heterocycloalkyl (e.g., pyrrolidinyl (for example             pyrrolidin-3-yl or pyrrolidin-1-yl), piperidinyl (for             example, piperidin-1-yl), morpholinyl),         -   —C₀₋₆alkylaryl (e.g., phenyl or benzyl) or         -   —C₀₋₆alkylheteroaryl (e.g., pyrid-4-yl, pyrid-2-yl or             pyrazol-3-yl)             -   wherein said aryl or heteroaryl is optionally                 substituted with one or more halo (e.g.,                 4-fluorophenyl), hydroxy (e.g., 4-hydroxyphenyl),                 C₁₋₆alkyl, C₁₋₆alkoxy or another aryl group (e.g.,                 biphenyl-4-ylmethyl);

    -   (vi) R₆ is H, C₁₋₆alkyl (e.g., methyl or ethyl) or         C₃₋₈cycloalkyl;

    -   (vii) R₁₄ and R₁₈ are independently H or C₁₋₆alkyl,         in free or salt form.

In still another embodiment, the invention provides that the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are Formula X, e.g.:

-   -   wherein     -   (i) Q is —C(═S)—, —C(═O)—, —C(═N(R₇))— or —C(R₁₄)(R₁₅)—;     -   (ii) R₁ is H or C₁₋₆alkyl (e.g., methyl or ethyl);     -   (iii) R₂ is H, C₁₋₆alkyl (e.g., isopropyl, isobutyl,         2-methylbutyl, 2,2-dimethylpropyl) wherein said alkyl group is         optionally substituted with halo (e.g., fluoro) or hydroxy         (e.g., 1-hydroxypropan-2-yl, 3-hydroxy-2-methylpropyl), for         example, R₂ may be a trifluoromethyl or 2,2,2-trifluoroethyl,         N(R₁₄)(R₁₅)— C₁₋₆alkyl (e.g., 2-(dimethylamino)ethyl or         2-aminopropyl), arylC₁₋₆alkyl (e.g., phenyl or benzyl),         heteroaryl C₁₋₆alkyl (e.g., pyridinylmethyl),         C₁₋₆alkoxyaryl-C₁₋₆alkyl (e.g., 4-methoxybenzyl); -G-J wherein:         -   G is a single bond or, alkylene (e.g., methylene); J is             cycloalkyl or heterocycloalkyl (e.g., oxetan-2-yl,             pyrolyin-3-yl, pyrolyin-2-yl) optionally substituted with             one or more C₁₋₆alkyl (e.g., (1-methylpyrolidin-2-yl)),             amino (e.g., —NH₂), for example, -G-J may be             —C₀₋₄alkyl-C₃₋₈cycloalkyl (e.g., cyclopentyl, cyclohexyl or             cyclopropylmethyl) optionally substituted with one or more             C₁₋₆alkyl, amino (e.g., —NH₂), for example,             2-aminocyclopentyl or 2-aminocyclohexyl, wherein said             cycloalkyl optionally contains one or more heteroatom             selected from N and O (e.g., pyrrolidinyl, for example,             pyrrolidin-3-yl or pyrrolidin-2-yl,             1-methyl-pyrrolindin-2-yl, 1-methyl-pyrrolindin-3-yl,             1-methyl-pyrrolindin-2-yl-methyl or             1-methyl-pyrrolindin-3-yl-methyl);     -   (iv) R₃ is     -   1) -D-E-F wherein:         -   D is a single bond, C₁₋₆alkylene (e.g., methylene), or             arylalkylene         -   (e.g., p-benzylene or —CH₂C₆H₄—);         -   E is a single bond,         -   C₁₋₆alkylene (e.g., methylene) C₂₋₆alkynylene (e.g.,             ethynylene, prop-2-yn-1-ylene), ethynylene,             prop-2-yn-1-ylene), —C₀₋₄alkylarylene (e.g., phenylene or             —C₆H₄—, -benzyle{acute over (η)}ε- or —CH₂C₆H₄—), wherein             the arylene group is optionally substituted with halo (e.g.,             Cl or F), heteroarylene (e.g., pyridinylene or             pyrimidinylene), aminoC₁₋₆alkylene (e.g., —CH₂N(H)—), amino             (e.g., —N(H)—);         -   C₃₋₈cycloalkylene optionally containing one or more             heteroatom selected from N or O (e.g., piperidinylene),         -   F is         -   H,         -   halo (e.g., F, Br, Cl), C₁₋₆alkyl (e.g., isopropyl or             isobutyl), haloC₁₋₆alkyl (e.g., trifluoromethyl),         -   aryl (e.g., phenyl),         -   C₃₋₈cycloalkyl optionally containing at least one atom             selected from a group consisting of N or O (e.g.,             cyclopentyl, N cyclohexyl, piperidinyl, pyrrolidinyl,             tetrahydro-2H-pyran-4-yl, or morpholinyl), said cycloalkyl             is optionally substituted with C₁₋₆alkyl (e.g., methyl or             isopropyl), for example, 1-methylpyrrolidin-2-yl,             pyrrolidin-1-yl, pyrrolidin-2-yl, piperidin-2-yl,             1-methyrpiperidin-2-yl, 1-ethylpiperidin-2-yl, heteroaryl             optionally substituted with C₁₋₆alkyl, (e.g., pyridyl, (for             example, pyrid-2-yl), pyrimidinyl (for example,             pyrimidin-2-yl), thiadiazolyl (for example,             1,2,3-thiadiazol-4-yl), diazolyl (e.g., pyrazolyl (for             example, pyrazol-1-yl) or imidazolyl (for example,             imidazol-1-yl, 4-methylimidazolyl, 1-methylimidazol-2-yl,),             triazolyl (e.g., 1,2,4-triazol-1-yl), tetrazolyl (e.g.,             tetrazol-5-yl), alkoxadiazolyl (e.g.,             5-methyl-1,2,4-oxadiazol), pyrazolyl (e.g., pyrazol-1-yl),             wherein said         -   heteroaryl is optionally substituted with halo (e.g.,             fluoro) or haloC₁₋₆alkyl, for example, 6-fluoropyrid-2-yl;             amino (e.g., —NH₂), C₁₋₆alkoxy, —O-haloC₁₋₆alkyl (e.g.,             —O—CF₃), C₁₋₆alkylsulfonyl (for example, methylsulfonyl or             —S(O)₂CH₃),         -   —C(O)—R₁₃,         -   —N(R₁₄)(R₁₅); or         -   2) a substituted heteroarylaklyl, e.g., substituted with             haloalkyl; or         -   3) attached to the nitrogen on the pyrrolo portion of             Formula I and is a moiety of Formula A

-   -   wherein X, Y and Z are, independently, N or C, and R₈, R₉, R₁ 1         and R₁₂ are independently H or halogen (e.g., Cl or F); and R₁₀         is halogen, C₁₋₆alkyl,     -   C₁₋₆alkoxy (e.g., methoxy), C₃₋₈cycloalkyl, heteroC₃₋₈cycloalkyl         (e.g., pyrrolidinyl) haloC₁₋₆alkyl (e.g., trifluoromethyl), aryl         (e.g., phenyl), heteroaryl (e.g., pyridyl, (for example,         pyrid-2-yl) or e.g., thiadiazolyl (for example,         1,2,3-thiadiazol-4-yl), diazolyl (e.g., imidazolyl or         pyrazolyl), triazolyl (e.g., 1,2,4-triazol-1-yl), tetrazolyl         (e.g., tetrazol-5-yl), alkoxadiazolyl (e.g.,         5-methyl-1,2,4-oxadiazol), pyrazolyl (e.g., pyrazol-1-yl),         C₁₋₆alkyl sulfonyl (e.g., methyl sulfonyl), arylcarbonyl (e.g.,         benzoyl), heteroarylcarbonyl,     -   alkoxycarbonyl, (e.g., methoxycarbonyl), aminocarbonyl; wherein         the aryl, heteroaryl, cycloalkyl or heterocycloalkyl is         optionally substituted with one or more C₁₋₆alkyl (e.g.,         methyl), halogen (e.g., chloro or fluoro), haloC₁₋₆alkyl (e.g.,         trifluoromethyl), hydroxy, carboxy, —SH, or an additional aryl         or heteroaryl (e.g., biphenyl or pyridylphenyl) preferably R₁₀         is phenyl or pyridyl, e.g., 2-pyridyl optionally substituted         with the substituents previously defined;     -   provided that when X, Y or X is nitrogen, R₈, R₉ or R₁₀,         respectively, is not present; (v) R₄ and R₅ are independently H,         C₁₋₆alkyl (e.g., methyl, isopropyl),     -   C₃₋₈cycloalkyl (e.g., cyclopentyl), C₃₋₈heterocycloalkyl (e.g.,         pyrrolidin-3-yl), aryl (e.g., phenyl) or heteroaryl (e.g.,         pyrid-4-yl, pyrid-2-yl or pyrazol-3-yl) wherein said aryl or         heteroaryl is optionally substituted with halo (e.g.,         4-fluorophenyl), hydroxy (e.g., 4-hydroxyphenyl), C₁-6alkyl,         C₁₋₆alkoxy or another aryl group (e.g., biphenyl-4-ylmethyl);     -   (vi) R₆ is H, C₁₋₆alkyl (e.g., methyl), hydroxy, C₁₋₆alkoxy,         aryloxy, —N(R₁₆)(R₁₇), oxo (e.g., ═O), or C₃₋₈Cycloalkyl;     -   (vii) R₇ is H, C₁₋₆alkyl (e.g., methyl) or C₃₋₈cycloalkyl         wherein said cycloalkyl is optionally substituted with one or         more oxo (e.g., 2,5-dioxopyrrolidin-1-yl); (viii) R₁₃ is         —N(R₁₄)(R₁₅), C₁₋₆alkyl (e.g., methyl), —OC₁₋₆alkyl (e.g.,         —OCH₃), haloC₁₋₆alkyl (trifluoromethyl), aryl (e.g., phenyl), or         heteroaryl; and     -   (ix) R₁₄ and R₁₅ are independently H or C₁₋₆alkyl;     -   (x) R₁₆ and R₁₇ are independently H, C₁₋₆alkyl, aryl (e.g.,         phenyl), heteroaryl, wherein said aryl or heteroaryl is         optionally substituted with halo (e.g., fluoro), C₁₋₆alkoxy         (e.g., methoxy); in free or salt form.

In one embodiment the invention provides that the PDE1 inhibitors for use in the methods of treatment and prophylaxis described herein are Formula XI:

wherein

-   -   (i) L is S, SO or SO₂;     -   (ii) R₂ is H or C₁₋₆alkyl (e.g., methyl or ethyl);     -   (iii) R₂ is     -   H,     -   C₁₋₆alkyl (e.g., isopropyl, isobutyl, neopentyl, 2-methylbutyl,         2,2-dimethylpropyl) wherein said alkyl group is optionally         substituted with halo (e.g., fluoro) or hydroxy (e.g.,         1-hydroxypropan-2-yl, 3-hydroxy-2-methylpropyl),         —C₀₋₄alkyl-C₃₋₈cycloalkyl (e.g., cyclopentyl, cyclohexyl)         optionally substituted with one or more amino (e.g., —NH₂), for         example, 2-aminocyclopentyl or 2-aminocyclohexyl), wherein said         cycloalkyl optionally contains one or more heteroatom selected         from N and O and is optionally substituted with C₁₋₆alkyl (e.g.,         1-methyl-pyrrolindin-2-yl, 1-methyl-pyrrolindin-3-yl,         1-methyl-pyrrolindin-2-yl-methyl or         1-methyl-pyrrolindin-3-yl-methyl), C₃₋₈heterocycloalkyl (e.g.,         pyrrolidinyl, for example, pyrrolidin-3-yl) optionally         substituted with C₁₋₆alkyl (e.g., methyl), for example,         1-methylpyrrolidin-3-yl, C₃₋₈cycloalkyl-C₁₋₆alkyl (e.g.,         cyclopropylmethyl), haloC₁₋₆alkyl (e.g., trifluoromethyl,         2,2,2-trifluoroethyl), —N(R₁₄)(R₁₅)—C₁₋₆alkyl (e.g.,         2-(dimethylamino)ethyl, 2-aminopropyl), hydroxyC₁₋₆alkyl (e.g.,         (e.g., 3-hydroxy-2-methylpropyl, 1-hydroxyprop-2-yl),         arylC₀₋₆alkyl (e.g., benzyl), heteroarylC₁₋₆alkyl (e.g.,         pyridinylmethyl), C₁₋₆alkoxyarylC₁₋₆alkyl (e.g.,         4-methoxybenzyl); -G-J wherein: G is a single bond or, alkylene         (e.g., methylene);     -   J is cycloalkyl or heterocycloalkyl (e.g., oxetan-2-yl,         pyrolyin-3-yl, pyrolyin-2-yl) optionally substituted with         C₁₋₆alkyl (e.g., (1-methylpyrolidin-2-yl));     -   (iv) R₃ is attached to one of the nitrogens on the pyrazolo         portion of Formula I and is a moiety of Formula A

wherein X, Y and Z are, independently, N or C, and R₈, R₉, R₁₁ and R₁₂ are independently H or halogen (e.g., Cl or F); and R₁₀ is halogen, C₁₋₆alkyl, C₃₋₈cycloalkyl, heteroC₃₋₈cycloalkyl (e.g., pyrrolidinyl or piperidinyl) haloC₁₋₆alkyl (e.g., trifluoromethyl), aryl (e.g., phenyl), heteroaryl (e.g., pyridyl, (for example, pyrid-2-yl) or e.g., thiadiazolyl (for example, 1,2,3-thiadiazol-4-15 yl), diazolyl, triazolyl (e.g., 1,2,4-triazol-1-yl), tetrazolyl (e.g., tetrazol-5-yl), alkoxadiazolyl (e.g., 5-methyl-1,2,4-oxadiazol), pyrazolyl (e.g., pyrazol-i-yl), alkyl sulfonyl (e.g., methyl sulfonyl), arylcarbonyl (e.g., benzoyl), or heteroarylcarbonyl, alkoxycarbonyl, (e.g., methoxycarbonyl), aminocarbonyl; preferably phenyl, pyridyl, e.g., 2-pyridyl, piperidinyl, or pyrrolidinyl; wherein the aryl, heteroaryl cycloalkyl or heterocycloalkyl is optionally substituted with one or more halo (e.g., F or Cl), C₁₋₆alkly, C₁₋₆alkoxy, C₁₋₄haloalkyl (e.g., trifluoromethyl), and/or —SH, provided that when X, Y or X is nitrogen, R₈, R₉ or R₁₀, respectively, is not present; (v) R₄ is H, C₁₋₆alkyl (e.g., methyl, isopropyl), C₃₋₈cycloalkyl (e.g., cyclopentyl), C₃₋₈heterocycloalkyl (e.g., pyrrolidin-3-yl), aryl (e.g., phenyl) or heteroaryl (e.g., pyrid-4-yl, pyrid-2-yl or pyrazol-3-yl) wherein said aryl or heteroaryl is optionally substituted with halo (e.g., 4-fluorophenyl), hydroxy (e.g., 4-hydroxyphenyl), C₁₋₆alkyl, C₁₋₆alkoxy or another aryl group (e.g., biphenyl-4-ylmethyl); (vi) R₁₄ and R₁₅ are independently H or C₁₋₆alkyl, in free or salt form.

The invention further provides the use of PDE1 inhibitors of any of the preceding formulae (e.g., Formula I, II, III, IV, V, VI, VII, VIII, IX, X, XI), wherein the compound is selected from any of the following:

In one embodiment, preferred compounds of the any of the preceding formulae (e.g., Formula I, II, III, IV, V, VI, VII, VIII, IX, X, XI) are compounds that inhibit phosphodiesterase-mediated (e.g., PDE1-mediated, especially PDE1A or PDE1C-mediated) hydrolysis of cGMP, e.g., the preferred compounds have an IC₅₀ of less than 1 μM, preferably less than 500 nM, preferably less than 50 nM, and preferably less than 5 nM in an immobilized-metal affinity particle reagent PDE assay, in free or salt form.

In another embodiment, the preferred PDE1 inhibitors of any of the preceding formulae (e.g., Formula I, II, III, IV, V, VI, VII, VIII, IX, X, XI) are compounds selected from the following:

In a further embodiment, the preferred PDE1 inhibitors are selective for PDE1 (generally, off-target interactions are greater than 100× lower than affinity for PDE1), exhibit good oral bioavailability, and exhibit minimal brain penetration (e.g., blood/plasma concentration ratios of less than 0.4, more preferably less than 0.2).

In another aspect, the present invention also includes the novel combination of any of the PDE1 inhibitors of the preceding formulae (e.g., Formula I, II, III, IV, V, VI, VII, VIII, IX, X, XI) with any selective NEP inhibitor. In a preferred embodiment, the aforementioned PDE1 inhibitor is a selective PDE1 inhibitor.

In another embodiment of the present invention, the PDE1 inhibitor is a 1,3,5-substituted 6,7-dihydro-1H-pyrazolo[4,3-d]pyrimidin-7-one, of formula XV:

wherein:

-   -   R_(a) is methyl or C₂-C₆ alkyl;     -   R₁ is H or C₁-C₄ alkyl; each of R₂ and R₃ is independently         selected from H and C₁-C₄ alkyl, or R₂ is H or C₁-C₄ alkyl and         R₃ is OH, C₂-C₄ alkanoyloxy or fluoro, or R₂ and R₃ when taken         together represent C₂-C₆ alkylene, or R₂ and R₃ when taken         together with the carbon atom to which they are attached         represent a carbonyl group;     -   Ar is either (a)

-   -   -   wherein each of R₄, R₅ and R₆ is independently selected from             H         -   C₁-C₄ alkyl,         -   C₁-C₄ alkoxy,         -   C₁-C₄ alkoxy-Z—, halo, halo(C₁-C₄)alkyl, phenoxy, optionally             substituted by up to three substituents each of which             substituent is independently selected from halo, C₁₋₄ alkyl,             and C₁-C₄ alkoxy, nitro, hydroxy, hydroxy-Z—,         -   C₂-C₄ alkanoyl, amino, amino-Z—, (C₁-C₄ alkyl)NH,         -   (C₁-C₄ alkyl)₂N—,         -   (C₁-C₄ alkyl)NH—Z—,         -   (C₁-C₄ alkyl)₂N—Z—,         -   —COOH, —Z—COOH,         -   —COO(C₁-C₄ alkyl),         -   —Z—COO(C₁-C₄ alkyl)         -   C₁-C₄ alkanesulfonamido,         -   C₁-C₄ alkanesulfonamido-Z—, halo(C₁-C₄)alkanesulfonamido,             halo(C₁-C₄)alkanesulfonamido-Z—, C₁-C₄ alkanamido,         -   C₁-C₄ alkanamido-Z—,         -   HOOC—Z—NH—,         -   HOOC—Z—NH—Z—, (C₁-C₄ alkyl)OOC—Z—NH—,         -   (C₁-C₄ alkyl)OOC—Z—NH—Z—,         -   C₁-C₄ alkyl-NH—SO₂—NH—,         -   C₁-C₄ alkyl-NH—SO₂—NH—Z—,         -   (C₁-C₄ alkyl)₂-N—SO₂—NH—, (C₁-C₄ alkyl)₂-N—SO₂—NH—Z—,         -   C₁-C₄ alkoxy CH═CH—Z—CONH—,         -   C₁-C₄ alkoxy CH═CHCONH         -   C₁-C₄ alkyl-SO₂—N(C₁-C₄ alkyl)-,         -   C₁-C₄ alkyl-SO₂—N(C₁-C₄ alkyl)-Z—, (C₁-C₄             alkyl)NH—Z—SO₂—NH—,         -   (C₁-C₄ alkyl)₂N—Z—SO₂—NH—,         -   (C₁-C₄ alkyl)NH—Z—SO₂—NH—Z—,         -   (C₁-C₄ alkyl)₂N—Z—SO₂—NH—Z—, benzenesulfonamido, optionally             ring substituted by up to three substituents each of which             is independently selected from halo, C₁₋₄ alkyl, and         -   C₁-C₄ alkoxy,         -   C₁-C₄ alkanoyl-N(C₁-C₄ alkyl)-,         -   C₁-C₄ alkanoyl-N(C₁-C₄ alkyl)-Z—,         -   C₁-C₄ alkoxycarbonyl-CH(CH₂OH)NHSO₂—, —SO₃H,         -   —SO₂NH₂,         -   H₂NOC—CH(CH₂OH)—NHSO₂—,         -   HOOC—Z—O—, and         -   (C₁-C₄ alkyl)OOC—Z—O—, or optionally one of R₄, R₅ and R₆ is             a G-Het group and wherein the others of R₄, R₅ and Re are             independently selected from the R₄, R₅ and R₆ substituents             listed above;         -   Z is C₁-C₄ alkylene,         -   G is a direct link, Z, O, —SO₂NH—, SO₂, or —Z—N(C₁-C₄             alkyl)SO₂—,         -   Het is a 5- or 6-membered heterocyclic group containing 1,             2, 3 or 4 nitrogen heteroatoms; or 1 or 2 nitrogen             heteroatoms and 1 sulfur heteroatom or         -   1 oxygen heteroatom; or the heterocyclic group is furanyl or             thiophenyl; wherein the Het group is saturated or partially             or fully unsaturated and optionally substituted by up to 3             substituents, wherein each substituent is independently             selected from C₁-C₄ alkyl, oxo, hydroxy, halo, and             halo(C₁-C₄) alkyl;

    -   or (b) any one of the following bicyclic groups:         -   benzodioxolanyl, benzodioxanyl, benzimidazolyl, quinolinyl,             indolyl, quinazolinyl, isoquinolinyl, benzotriazolyl,             benzofuranyl, benzothiophenyl, quinoxalinyl, or             phthalizinyl, wherein said bicyclic Ar groups are linked to             the neighboring —C(R₂R₃)— group via the benzo ring portion,         -   and wherein the heterocyclic portion of said bicyclic Ar             group is optionally partially or fully saturated, said group             being optionally substituted by one or more of C₁-C₄ alkyl,             halo, hydroxy, oxo, amino, and C₁-C₄ alkoxy;             or a pharmaceutically acceptable salt of the compound, or a             pharmaceutically acceptable solvate of the compound or the             salt.

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XV of the following formulae:

-   -   3.2 Of Formula XV wherein R_(a) is a C₂₋₅ alkyl group;     -   3.3 Of Formula XV wherein R₃ is a C₂₋₄ alkyl group.     -   3.4 Of Formula XV wherein R₃ is a C₃ alkyl group.     -   3.5 Of Formula XV wherein R₃ is methyl     -   3.6 Of Formula XV, 3.2, 3.3, 3.4 or 3.5 wherein R₁ is a C₁₋₆         alkyl group.     -   3.7 Of any of the preceding formulae wherein R₁ is a C₁₋₃ alkyl         group.     -   3.8 Of any of the preceding formulae wherein R₁ is a methyl         group.     -   3.9 Of any of the preceding formulae wherein R₂ is H.     -   3.10 Of any of the preceding formulae wherein R₃ is H.     -   3.11 Of any of the preceding formulae wherein R₄, R₅ and R₆ are         independently selected from H, (C₁₋₄ alkyl)₂N—, C₁₋₄         alkanesulphonamido and benzenesulfonamido.     -   3.12 Of any of the preceding formulae wherein R₄, R₅ and R₆ are         independently selected from H, diethylamino, methanesulfonamido         and benzenesulfonamido.     -   3.13 Of any of the preceding formulae wherein Ar is         4-diethylaminophenyl.     -   3.14 Of any of the preceding formulae wherein Ar is         2-methanesulfonamido-phenyl.     -   3.15 Of any of the preceding formulae wherein Ar is         4-benzenesulfonamido-phenyl     -   3.16 Of any of the preceding formulae wherein one of R₄, R₅ and         R₆ is (C₁₋₄ alkyl)₂N- and wherein the other two of R₄, R₅ and R₆         are H.     -   3.17 Of any of the preceding formulae wherein one of R₄, R₅ and         R₆ is diethylamino and wherein the other two of R₄, R₅ and R₆         are H.     -   3.18 Of any of the preceding formulae wherein R₃ is methyl.     -   3.19 Of any of the preceding formulae wherein R₃ is C₂-C₆ alkyl.     -   3.20 Of any of the preceding formulae wherein the compound is         selected from the following:

-   -   3.21 Of any of the preceding formulae wherein the compound is

-   -   3.22 A compound which is a 1,3,5,-substituted,         6,7-dihydro-1H-pyrazolo[4,3-flf]pyrimidin-7-one, in free or         pharmaceutically acceptable salt form, e.g. a compound of         Formula XV or according to any of formulae 3.2-3.21, wherein the         compound inhibits phosphodiesterase-mediated (e.g.,         PDE1-mediated) hydrolysis of cGMP, e.g., with an IC₅₀ of less         than 1 LM, preferably less than 25 nM.

In another embodiment of the present invention, the PDE1 inhibitor is a substituted imidazo[2,1-b]purin-4-one of Formula XVII-a or XVII-b:

in free, salt or prodrug form, including its enantiomers, diastereomers and racemates, wherein:

-   -   (i) q=0, 1 or 2;     -   (ii) R¹, R^(a), R^(b), R^(c) and R^(d) are each independently H,         alkyl, aryl, heteroaryl, cycloalkyl or heterocycloalkyl groups,         wherein each alkyl group of R¹, R^(a), R^(b), R^(c) and R^(d) is         independently unsubstituted or substituted with 1 to 5         independently selected R³ moieties which can be the same or         different, each R³ moiety being independently selected from the         group consisting of hydroxy, alkoxy, cycloalkoxy, aryloxy,         alkylthio, arylthio, aryl, haloaryl, heteroaryl, cycloalkyl,         heterocycloalkyl, amino, alkylamino, dialkylamino,         cycloalkylamino and heterocycloalkylamino groups;     -   wherein each of the aryl, heteroaryl, cycloalkyl and         heterocycloalkyl groups of R¹, R^(a), R^(b), R^(c) and R^(d) is         independently unsubstituted or substituted with 1 to 5         independently selected R⁴ moieties which can be the same or         different, each     -   R⁴ moiety being independently selected from the group consisting         of: halo, optionally substituted aryl (e.g., phenyl,         chlorophenyl, methoxyphenyl), heteroaryl (e.g., pyridyl,         pyrrolyl), nitro, cyano, haloalkyl, haloalkoxy, alkyl, alkoxy,         cycloalkyl, heterocycloalkyl (e.g., pyrrolidinyl,         morpholin-4-yl, pyrrol-1-yl), cycloalkylalkyl, amino,         alkylamino, dialkylamino, —OCF₃, acyloxy, —OR⁸, —C(O)R⁹,         —C(O)OR⁸, —NR¹⁰C(O)R⁹, —NR¹⁰C(O)OR⁸, —NR¹⁰S(O)₂R₉, —S(O)₀₋₂R⁹         groups, carbonyl when two hydrogens attached to the same carbon         atom of the cycloalkyl or heterocycloalkyl group of R′ are         substituted, and ═CR⁸R⁹ when two hydrogens attached to the same         carbon atom of the cycloalkyl or heterocycloalkyl groups of R¹         are substituted,     -   wherein each of the aryl, heteroaryl, cycloalkyl and         heterocycloalkyl groups of the R³ and R⁴ moieties above is         independently unsubstituted or substituted with 1 to 5         independently selected R¹² moieties which can be the same or         different, each R¹² moiety being independently selected from the         group consisting of: halo, phenyl, nitro, cyano, haloalkyl,         haloalkoxy, alkyl, cycloalkyl, cycloalkylalkyl, amino,         alkylamino, —OCF₃, acyloxy, —OR⁸, —C(O)R⁹, —C(O)OR⁸,         —NR¹⁰C(O)R⁹, —NR¹⁰C(O)OR⁸, —NR¹⁰S(O)₂R₉, —S(O)₀₋₂R⁹ groups,         carbonyl when two hydrogens attached to the same carbon atom of         the cycloalkyl or heterocycloalkyl group of R or R⁴ are         substituted, and ═CR⁸R⁹ when two hydrogens attached to the same         carbon atom of the cycloalkyl or heterocycloalkyl group of R³ or         R⁴ are substituted; or     -   (iii) R^(a) and R^(b), together with the carbon to which they         are both attached, form a 4- to 7-membered cycloalkyl or         heterocycloalkyl ring, and R^(c) and R^(d) are each         independently H or an alkyl group; or     -   (iv) R^(a) and R^(c), together with the respective carbons to         which they are attached, form a 4- to 7-membered cycloalkyl or         heterocycloalkyl ring, and R^(b) and R^(d) are each         independently H or an alkyl group, preferably R^(a) and R^(c)         together have the cis configuration, e.g., where the carbons         carrying R^(a) and R^(c) have the R and S configurations,         respectively;     -   (v) R² is H, halo, alkyl, haloalkyl, alkoxy, alkylthio, amino,         aminosulfonyl, monoalkylamino, dialkylamino, hydroxyalkylamino,         aminoalkylamino, carboxy, alkoxycarbonyl, aminocarbonyl or         alkylaminocarbonyl group,     -   wherein each alkyl group of R is independently unsubstituted or         substituted with 1 to 5 independently selected R¹³ moieties         which can be the same or different, each R¹³ moiety being         independently selected from the group consisting of halo,         hydroxy, alkoxy, alkyl, aryl (e.g., phenyl, napthyl) heteroaryl         (e.g., 1H-imidazol-2-yl), cycloalkyl, heterocycloalkyl (e.g.,         pyrolidin-1-yl), amino, monoalkylamino or dialkylamino group,     -   wherein each aryl group of R¹³ is independently unsubstituted or         substituted with 1 to 5 independently selected R⁴ moieties which         can be the same or different;     -   (vi) Y is H or an alkyl group substituted with (i) an aryl,         heteroaryl, cycloalkyl, hydroxy, alkoxy, amino, monoalkylamino         or dialkylamino group, or (ii) an aryl group substituted with         from one to three moieties each independently selected from the         group consisting of: halo, alkyl, phenyl, hydroxy, alkoxy,         phenoxy, amino, monoalkylamino and dialkylamino group;     -   (vii) each R⁸ is independently H, alkyl or aryl;     -   (viii) each R⁹ is independently H, alkyl, aryl or —N¹⁰R¹¹;     -   (ix) each R¹⁰ is independently H, alkyl, aryl, heteroaryl,         arylalkyl or heteroarylalkyl, wherein each alkyl, aryl,         heteroaryl, arylalkyl or heteroarylalkyl of R¹⁰ is unsubstituted         or independently substituted with 1 to 5 R¹⁴ moieties which can         be the same or different, each R¹⁴ moiety being independently         selected from the group consisting of: halo, alkyl, aryl,         cycloalkyl, —CF₃, —OCF₃, —CN, —OR⁸, —CH₂OR⁸, —C(O)OR⁸ and         —C(O)NR⁸R⁸; and     -   (x) each R¹¹ is independently H, alkyl, aryl, heteroaryl,         arylalkyl or heteroarylalkyl, wherein each alkyl, aryl,         heteroaryl, arylalkyl or heteroarylalkyl of R¹¹ is unsubstituted         or independently substituted with 1 to 5 R¹⁴ moieties which can         be the same or different;         and wherein the numbering of the ring system of the Formula         XVII-a or XVII-b is, for example, as follows for q=0 and q=1,         respectively:

In another embodiment of the present invention, the PDE1 inhibitor is a compound according to Formula XVII-a or XVII-b, in free or salt form, as follows:

-   -   4.1: Formula XVII-a or XVII-b, wherein q=0, 1 or 2;     -   4.2: Formula XVII-a or XVII-b, wherein q=0;     -   4.3: Formula XVII-a or XVII-b or 4.1 or 4.2, wherein R¹ is         alkyl;     -   4.4: Formula XVII-a or XVII-b or 4.1-4.2, wherein R¹ is methyl;     -   4.5: Formula XVII-a or XVII-b or 4.1-4.4, wherein R^(a) and         R^(c), together with the respective carbons to which they are         attached, form a 4- to 7-membered cycloalkyl or heterocycloalkyl         ring, and R^(b) and R^(d) are each independently H or an alkyl         group;     -   4.6: Formula XVII-a or XVII-b or 4.1-4.4, wherein R^(a) and         R^(c), together with the respective carbons to which they are         attached, form a 5-membered heterocycloalkyl ring, and R^(b) and         R^(d) are each independently H;     -   4.7: Formula XVII-a or XVII-b or 4.1-4.4, wherein R^(a) and         R^(b), together with the respective carbons to which they are         attached, form a 5-membered heterocycloalkyl ring, and R^(c) and         R^(d) are each independently H;     -   4.8: Formula XVII-a or XVII-b or 4.1-4.7, wherein R² is alkyl or         haloalkyl;     -   4.9: Formula XVII-a or XVII-b or 4.1-4.7, wherein R² is         biphenyl-4-ylmethyl;     -   4.10: Formula XVII-a or XVII-b or 4.1-4.7, wherein R² is benzyl;     -   4.11: Formula XVII-a or XVII-b or 4.1-4.7, wherein R² is         cyclopentylmethyl;     -   4.12: Formula XVII-a or XVII-b or 4.1-4.7, wherein R² is         cyclopropylmethyl;     -   4.13: Formula XVII-a or XVII-b or 4.1-4.12, wherein Y is benzyl;         and/or     -   4.14: Of any of the preceding formulae wherein the compound is         selected from the following:

-   -   4.15: Of any of the preceding formulae wherein the compound is

-   -   4.16: A compound which is a substituted         imidazo[2,1-b]purin-4-one, in free or pharmaceutically         acceptable salt form, e.g. a compound of Formula XVII-a or         XVII-b according to any of formulae 4.1-4.15, wherein the         compound inhibits phosphodiesterase-mediated (e.g.,         PDE1-mediated) hydrolysis of cGMP, e.g., with an IC₅₀ of less         than 1 μM, preferably less than 25 nM.

In another embodiment of the present invention, the PDE1 inhibitor is preferably a compound of Formula XVII-a or XVII-b are selected from a group consisting of:

-   (6aR,9aS)-5,6a,7,8,9,9a-hexahydro-5-methyl-2,3-bis(phenylmethyl)cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one, -   (6aR,9aS)-2-(biphenyl-4-ylmethyl)-5,6a,7,8,9,9a-hexahydro-5-methyl-3-(phenylmethyl)cyclopent[4,5]imidazo[2,1b]purin-4(3H)-one, -   5′-methyl-2′,3′-bis(phenylmethyl)spiro[cyclopentane-1,7′(8′H)-[3H]imidazo[2,1b]-purin]-4′(5′H)-one,     and -   5′-methyl-2′-(biphenyl-4-ylmethyl)-3′-(phenylmethyl)spiro-[cyclopentane-1,7′(8′H)-[3H]imidazo[2,1-b]purin]-4(5′H)-one,     in free or pharmaceutically acceptable salt form. In an especially     preferred embodiment, compound of Formula XVII-a is     (6aR,9aS)-2-(biphenyl-4-ylmethyl)-5,6a,7,8,9,9a-hexahydro-5-methyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one,     in free or salt form.

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XVIII-a or XVIII-b:

in free or salt form, wherein:

-   -   (i) J is oxygen or sulfur,     -   (ii) R¹ is hydrogen, alkyl or alkyl substituted with aryl or         hydroxy;     -   (iii) R² is hydrogen, aryl, heteroaryl, cycloalkyl, alkyl or         alkyl substituted with aryl, heteroaryl, hydroxy, alkoxy, amino,         monoalkyl amino or dialkylamino, or —(CH₂)_(m) TCOR²⁰ wherein m         is an integer from 1 to 6, T is oxygen or —NH— and R²⁰ is         hydrogen, aryl, heteroaryl, alkyl or alkyl substituted with aryl         or heteroaryl;     -   (iv) R³ is hydrogen, halo, trifluoromethyl, alkoxy, alkylthio,         alkyl, cycloalkyl, aryl, aminosulfonyl, amino, monoalkylamino,         dialkylamino, hydroxyalkylamino, aminoalkylamino, carboxy,         alkoxycarbonyl or aminocarbonyl or alkyl substituted with aryl,         hydroxy, alkoxy, amino, monoalkylamino or dialkylamino;     -   (v) R^(a), R^(b), R^(c) and R^(d) independently represent         hydrogen, alkyl, cycloalkyl or aryl; or (R^(a) and R^(b)) or         (R^(c) and R^(d)) or (R^(b) and R^(c)) can complete a saturated         ring of 5- to 7-carbon atoms, or (R^(a) and R^(b)) taken         together and (R^(b) and R^(c)) taken together, each complete a         saturated ring of 5- to 7-carbon atoms, wherein each ring         optionally can contain a sulfur or oxygen atom and whose carbon         atoms may be optionally substituted with one or more or the         following: alkenyl, alkynyl, hydroxy, carboxy, alkoxycarbonyl,         alkyl or alkyl substituted with hydroxy, carboxy or         alkoxycarbonyl; or such saturated ring can have two adjacent         carbon atoms which are shared with an adjoining aryl ring; and     -   (vi) n is zero or one.

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XVIII-a or XVIII-b, in free or salt form, as follows:

-   -   5.1: Formula XVIII-a or XVIII-b, wherein J=O.     -   5.2: Formula XVIII-a or XVIII-b or 5.1, wherein R¹ is alkyl.     -   5.3: Formula XVIII-a or XVIII-b, 5.1 or 5.2, wherein R² is         hydrogen, benzyl, 4-chlorobenzyl, cyclohexylmethyl or         trimethylacetoxymethyl.     -   5.4: Formula XVIII-a or XVIII-b, 5.1, 5.2 or 5.3, wherein R³ is         hydrogen, or alkyl such as methyl or ethyl.     -   5.5: Formula XVIII-a or XVIII-b, 5.1, 5.2, 5.3 or 5.4, wherein n         is zero; and     -   5.6: Formula XVIII-a or XVIII-b, 5.1, 5.2, 5.3, 5.4 or 5.5,         wherein R^(a) and R^(b) form a saturated 5 membered ring, or (R         and R^(c)) form a saturated 5, 6 or 7 membered ring, or (R^(a)         and R^(b)) and (R^(b) and R^(c)) each complete a saturated ring         and each ring contains 5 or 6 carbon atoms.

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XVIII-a or XVIII-b, in free or salt form, selected from the following:

-   cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-3-(phenylmethyl)cyclopenta[4,5]imidazo-[2,1-b]purin-4-one; -   7,8-Dihydro-5-methyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   cis-6a,7,8,9,10,10a-Hexahydro-5-methyl-3-(phenylmethyl)-3H-benzimidazo[2,1-b]purin-4(5H)-one; -   5,7,8,9-Tetrahydro-5-methyl-3-(phenylmethyl)pyrimido[2,1-b]purin-4(3H)-one; -   7,8-Dihydro-8-phenyl-5-methyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   5′,7′-Dihydro-5′-methyl-3′-(phenylmethyl)spiro[cyclohexane-1,8′-(8H)imidazo-[2,1-b]purin]4′(3H)-one; -   cis-5,6a,11,11a-Tetrahydro-5-methyl-3-(phenylmethyl)indeno[1′,2′:4,5]imidazo-[2,1-b]purin-4(3H)-one; -   5′,7′-Dihydro-2′,5′dimethyl-3′-(phenylmethyl)spiro     {cyclohexane-1,7′(8′H)-imidazo[2,1-b]purin}-4′-(3′H)-one; -   7,8-Dihydro-2,5,7,7,8(R,S)-pentamethyl-3H-imidazo[2,1-b]purin-4(5H)-one; -   cis-5,6a,7,11b-Tetrahydro-5-methyl-3-(phenylmethyl)indeno[2′,1′:4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-2,5-dimethyl-3-(phenylmethyl)cyclopent[4,5]-imidazo[2,1-b]purin-4-(3H)-one; -   5′-Methyl-3′-(phenylmethyl)-spiro[cyclopentane-1,7′-(8′H)-(3′H)imidazo[2,1-b]purin]-4-(5′H)-one; -   7,8-Dihydro-2,5,7,7-tetramethyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-7(R)-phenyl-2,5-dimethyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5-dimethyl-3,7(R)-bis(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   (+)-7,8-Dihydro-2,5-dimethyl-7-ethyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   6a(S)-7,8,9,10,10a(R)-Hexahydro-2,5-dimethyl-3-(phenylmethyl)-3H-benzimidazo[2,1-b]purin-4(5H)-one; -   6a(R)-7,8,9,10,10a(S)-hexahydro-2,5-dimethyl-3-(phenylmethyl)-3H-benzimidazo-[2,1     b]purin-4(5H)-one; -   7,8-Dihydro-2,5-dimethyl-7(R)-isopropyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5,7(R)-trimethyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   cis-7,7a,8,9,10,10a-Hexahydro-2,5-dimethyl-3-(phenylmethyl)-3H-cyclopenta-[5,6]pyrimido[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5-dimethyl-7(S)-(1-methylpropyl)-3-(phenylmethyl)-3H-imidazo-[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5-dimethyl-7(R)-(2-methylpropyl)-3-(phenylmethyl)-3H-imidazo-[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5-dimethyl-7(R,S)-(methoxycarbonyl)-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5-dimethyl-7(R,S)-(1-propyl)-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5-dimethyl-7(S)-(1-methylethyl)-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5,7,7,8(R,S)-pentamethyl-3H-imidazo[2,1-b]purin-4(5H)-one; -   5,7,8,9-Tetrahydro-2,5,7,9(R,S)-pentamethyl-3-(phenylmethyl)-pyrimido[2,1-b]purin-4(3H)-one; -   5,6a(R),7,8,9,9a(S)-Hexahydro-2,5-dimethyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   5,6a(S),7,8,9,9a(R)-Hexahydro-2,5-dimethyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-6a,7,8,9,10,10a-Hexahydro-2,5-dimethyl-3-(phenylmethyl)-3H-benzimidazo[2,1-b]purin-4(5H)-one; -   5¹,7′-Dihydro-2¹,5¹-dimethyl-3′-(phenylmethyl)spiro[cyclohexane-1,8-(8H)-imidazo[2,1-b]purin]-4-(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-2,5-dimethyl-3-(phenylmethyl)cyclohept-[6,7]imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-2-ethyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-6a,7,8,9,10,10a-Hexahydro-5-methyl-2-ethyl-3-(phenylmethyl)-3H-benzimidazo[2,1-b]purin-4-(5H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-2-ethyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-2-phenyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-6a,7,8,9,10,10a-Hexahydro-5-methyl-2-phenyl-3-(phenylmethyl)-3H-benzimidazo[2,1-b]purin-4(5H)-one; -   cis-5,6a,7,8.9,9a-Hexahydro-5-methylcyclopenta[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-2,5-dimethylcyclopenta[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a(R),     7,8,9,9a(S)-Hexahydro-2,5-dimethylcyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   2′,5′-dimethyl-spiro     {cyclopentane-1,7′-(8′H)-(3′H)-imidazo[2,1-b]purin}-4′(5′H)-one; -   7,8-Dihydro-2,5-dimethyl-7(R)-(1-methylethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5,7,7-tetramethyl-3H-imidazo[2,1-b]purin-4(5H)-one; -   7,8-Dihydro-2,5-dimethyl-7(S)-(1-methylethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   6a(R),7,8,9,10,10a(S)-Hexahydro-2,5-dimethyl-3H-benzimidazo[2,1-b]purin-4(5H)-one; -   5′,7′-Dihydro-2′,5′-dimethylspiro     {cyclohexane-1,7-(8′H)-imidazo[2,1-b]purin}-4′(3′H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-3-(phenylmethyl)cyclopenta[4,5]-imidazo[2,1-b]purin-4(3H)-thione; -   5,6a(R),7,8,9,9a(S)-Hexahydro-2,5-dimethyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-thione; -   cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-3-(4-chlorophenylmethyl)cyclopenta[4,5]-imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-3-(cyclohexylmethyl)cyclopent[4,5]-imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-3-(2-naphthylmethyl)cyclopent[4,5]-imidazo[2,1-b]purin-4(3H)-one; -   5,6a(R),7,8,9,9a(S)-Hexahydro-2,5-dimethyl-3-(4-bromophenylmethyl)-cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   5,6a(R)-7,8,9,9a(S)-Hexahydro-2,5-dimethyl-3-(4-methoxyphenylmethyl)-cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-2,3,5-trimethylcyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-2-(hydroxymethyl)-5-methyl-3-(phenylmethyl)-cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-2-methythio-5-methyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-3,4,5,6a,7,8,9,9a-Octahydro-5-methyl-4-oxo-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-2-carboxylic     acid; -   cis-3,4,5,6a,7,8,9,9a-Octahydro-5-methyl-4-oxo-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-2-carboxylic     acid, methyl ester; -   cis-5,6a,7,8,9,9a-Hexahydro-2-bromo-5-methyl-3-(phenylmethyl)cyclopent[4,5]imidazo[2,1-b]purin-4(3H)one; -   cis-5,6a,7,8,9,9a-Hexahydro-2-(methylaminosulfonyl)-5-methyl-3-(phenylmethyl)cyclopent[4,5]imidazo[2,1-b]purin-4(3H)one; -   cis-1-Cyclopentyl-5,6a,7,8,9,9a-hexahydro-5-methylcyclopent[4,5]imidazo[2,1-b]purin-4-(1H)one; -   cis-5,6a,7,8,9,9a-Hexahydro-3,5-bis-(phenylmethyl)cyclopent(4,5)imidazo(2,1-b)purin-4(3H)one; -   cis-6a,7,8,9,10,10a-Hexahydro-3,5-bis-(phenylmethyl)-3H-benzimidazo[2,1-b]purin-4(5H)one; -   cis-3-Cyclopentyl-5,6a,7,8,9,9a-hexahydro-5-methylcyclopent[4,5]imidazo(2,1-b)purin-4(3H)one; -   5′-Methyl-3′-(phenylmethy)spiro[cyclopentane-1,7-(8′H)-(3′H)imidazo[2,1-b]purin]-4-(5H)one; -   2¹,5′-Dimethyl-3¹-(phenylmethyl)-spiro[cyclopentane-1,7-(8′H)-(3H)imidazo[2,1-b]purin]-4-(5′H)one; -   cis-5,6a,(R)7,8,9,9a(S)-Hexahydro-5-methyl-3-(phenylmethyl)cyclopent[4,5]-imidazo(2,1-b)purin-4(3H)one; -   cis-3-Cyclopentyl-5,6a,7,8,9,9a-Hexahydro-2,5-dimethylcyclopent[4,5]imidazo-[2,1-b]purin-4(3H)one; -   5′-Methyl-2′-trifluoromethyl-3′-(phenylmethyl)spiro     {cyclo-pentane-1,7′(8′H)-(3′H)imidazo[2,1-b]purin}-4-(5′H)-one; -   7,8-Dihydro-5,7,7-trimethyl-2-trifluoromethyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(5H)-one; -   (+/−)-cis-5,6a,7,8,9,9a-Hexahydro-5-methyl-2-trifluoromethyl-3-(phenylmethyl)-cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   (+/−)-6a,7,8,9,9a,10,11,11a-Octahydro-2,5-dimethyl-3-(phenylmethyl)-3H-pentaleno[6a′,1′:4,5]imidazo[2,1-b]purin-4(5H)-one; -   (+)-6a,7,8,9,9a,10,11,11a-Octahydro-2,5-dimethyl-3-phenylmethyl-3H-pentaleno[6a′,1′:4,5]imidazo[2,1-b]purin-4(5H)-one; -   (−)-6a,7,8,9,9a,10,11,11a-Octahydro-2,5-dimethyl-3-phenylmethyl-3H-pentaleno[6a′,1′:4,5]Imidazo[2,1-b]purin-4(5H)-one; -   (+/−)     6a,7,8,9,9a,10,11,11a-Octahydro-2,5-dimethyl-3H-pentaleno[6a′,1′:4,5]-imidazo[2,1-b]purin-4(5H)-one; -   (+)-6a,7,8,9,9a,10,11,11a-Octahydro-2,5-dimethyl-3H-pentaleno[6a′,     1′:4,5]-imidazo[2,1-b]purin-4(5H)-one; -   (−)-6a,7,8,9,9a,     10,11,11a-Octahydro-2,5-dimethyl-3H-pentaleno[6a′,1′:4,5]-imidazo[2,1-b]purin-4(5H)-one; -   6a,7,8,9,10,10a,     11,12,13,13a-Decahydro-2,5-dimethyl-(3-phenylmethyl)-napth[1,8a-d]imidazo[2,1-b]purin-4(5H)one; -   7(R)-Cyclohexyl-7,8-dihydro-2,5-dimethyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(3H)-one; -   7(R)-Cyclohexyl-7,8-dihydro-2,5-dimethyl-3H-imidazo[2,1-b]purin-4(5H)-one; -   7(S)-Cyclohexyl-7,8-dihydro-2,5-dimethyl-3-(phenylmethyl)-3H-imidazo[2,1-b]purin-4(3H)-one; -   7(S)-Cyclohexyl-7,8-dihydro-2,5-dimethyl-3H-imidazo[2,1-b]purin-4(5H)-one; -   5,6a(R),7,8,9,9a(S)-Hexahydro-2,5-dimethyl-[3-(trimethylacetoxy)methyl]-cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   5,6a(R),7,8,9,9a(S)-Hexahydro-2,5-dimethyl-3-(4-pyridylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   5,6a(R),7,8,9,9a(S)-Hexahydro-2,5-dimethyl-3-[2-(4-morpholinyl)-ethyl]cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   5,6a(R),7,8,9,9a(S)-Hexahydro-2,5-dimethyl-3-[acetoxymethyl]cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   5,6a,7,8,9,9a-Hexahydro-2,5,6a-trimethyl-3-(phenylmethyl)cyclopent-[4,5]imidazo[2,1-b]purin-4(3H)-one; -   5,6a(R),7,8,9,9a(S)-Hexahydro-2,5,6a-trimethyl-3-(phenylmethyl)-cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   5,6a(S),7,8,9,9a(R)-Hexahydro-2,5,6a-trimethyl-3-(phenylmethyl)-cyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one; -   cis-6a,7,8,9,10,10a-Hexahydro-2,5,7-trimethyl-3-(phenylmethyl)-3H-benzimidazo[2,1-b]purin-4(5H)-one; -   cis-5,6a,7,8,9,9a-Hexahydro-2,5,6a-trimethylcyclopent[4,5]imidazo[2,1-b]purin-4(3H)-one;     or -   cis-[6a,7,8,9,10,10a-Hexahydro-2,5,7-trimethyl-3H-benzimidazo[2,1-b]purin-4(5H)-one].

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XIX-a or XIX-b:

or a pharmaceutically acceptable salt thereof, wherein,

-   -   (a) q=0 or 1;     -   (b) R¹ is H, cycloalkyl, alkyl, R²³-alkyl- or R²⁶.     -   (c) R^(a), R^(b) and R^(c) are, independently of one another,         each H, alkyl, cycloalkyl, aryl, R²²-aryl- or R²⁴-alkyl-; or         -   R^(a) and R^(b), together with the carbon to which they are             both attached, form a 4- to 7-membered ring, and R^(c) is H             or alkyl; or         -   R^(a) and R^(c), together with the respective carbons to             which they are attached, form a 4- to 7-membered ring, and             R^(b) is H or alkyl;     -   (d) for the group X—R²,         -   (i) X is a bond;         -   Y is aryl-alkyl or R²²-aryl-alkyl-; and         -   R² is monohaloalkyl, polyhaloalkyl, provided that it is not             trifluoromethyl, azido, cyano, oximino, cycloalkenyl,             heteroaryl, R²²-heteroaryl- or R²⁷-alkyl-; or         -   (ii) X is a bond;         -   Y is aryl-alkyl or R²²-aryl-alkyl-; and         -   R² is H, halo, —CONHR⁶, —CONR⁶R⁷, —CO₂R⁶, monohaloalkyl,             polyhaloalkyl, azido, cyano, —C═N—OR⁶, cycloalkyl,             cycloalkylalkyl, R²⁶, aminosulfonyl, alkyl or R²³-alkyl-; or         -   (iii) X is —O— or —S—;         -   Y is aryl-alkyl or R²²-aryl-alkyl-; and         -   R² is R²⁶, cycloalkyl, cycloalkylalkyl, heterocycloalkyl,             cycloalkenyl or R²⁶ alkyl-; or         -   (iv) X is —O— or —S—;         -   Y is aryl-alkyl or R²²-aryl-alkyl-; and R² is alkyl, R²⁶,             cycloalkyl, cycloalkylalkyl, heterocycloalkyl, cycloalkenyl             or R²⁸-alkyl-; or         -   (v) X is —SO— or —SO₂—;         -   Y is aryl-alkyl or R²²-aryl-alkyl-; and         -   R² is alkyl, R²⁶, cycloalkyl, cycloalkylalkyl,             heterocycloalkyl, cycloalkenyl or R²⁸-alkyl-; or         -   (vi) X is —NR⁸—;         -   Y is aryl-alkyl or R²²-aryl-alkyl-; and         -   R² is (R²⁹)_(p)-alkyl-, cycloalkyl, (R³⁰)_(p)-cycloalkyl-,             cycloalkenyl, (R³⁰)_(p)-cycloalkenyl-, heterocycloalkyl or             (R³⁰)_(p)-heterocycloalkyl-; or         -   (vii) X is —NR⁸—;         -   Y is aryl-alkyl or R²²-aryl-alkyl-; and         -   R² is alkyl, R²⁶, cycloalkyl, cycloalkylalkyl,             heterocycloalkyl, cycloalkenyl or R³¹-alkyl-; or         -   (viii) X is —C≡C—;         -   Y is aryl-alkyl or R²²-aryl-alkyl-; and         -   R² is alkyl, R²⁶, cycloalkyl, cycloalkylalkyl or R²³-alkyl-;     -   (e) wherein,         -   R⁶ is H or R₇;         -   R⁷ is alkyl, cycloalkyl or cycloalkylalkyl;         -   R⁸ is heterocycloalkyl or R⁶;         -   R²¹ is 1-6 substituents each independently selected from the             group consisting of halo, hydroxy, alkoxy, phenoxy, phenyl,             nitro, aminosulfonyl, cyano, monohaloalkyl, polyhaloalkyl,             thiol, alkylthio, cycloalkyl, cycloalkylalkyl, amino,             alkylamino, acylamino, carboxyl, —C(O)OR³⁴, carboxamido,             —OCF₃ and acyloxy;         -   R²² is 1-6 substituents each independently selected from the             group consisting of alkyl and R²¹;         -   R²³ is cycloalkoxy, aryloxy, alkylthio, arylthio, cycloalkyl             or R²⁸;         -   R²⁴ is cycloalkyl or R₂₆;         -   R²⁵ is hydroxy, alkoxy, amino, monoalkylamino, dialkylamino             or R²⁶         -   R²⁶ is aryl, R²²-aryl-, heteroaryl or R²²-heteroaryl-;         -   R²⁷ is cycloalkoxy, aryloxy, alkylthio, arylthio,             heteroaryl, R²²-heteroaryl-,         -   cycloalkyl, heterocycloalkyl, cycloalkenyl, cycloalkylamino             or         -   heterocyclo alkylamino;         -   R²⁸ is cycloalkylamino, heterocycloalkylamino or R²⁵;         -   R²⁹ is alkoxy, cycloalkylamino, heterocycloalkylamino or             R²⁶;         -   R³⁰ is halo, hydroxy, alkoxy, amino, aminosulfonyl, cyano,             monohaloalkyl,         -   polyhaloalkyl, thiol, alkylthio, alkyl, cycloalkyl,             cycloalkylalkyl or acyloxy;         -   R³¹ is cycloalkyl or R²⁸;         -   R³⁴ is alkyl, aryl, aralkyl and heteroaryl; and         -   p is 1 to 4.

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XIX-a or XIX-b, in free or salt form, selected from the following:

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XX:

in free or a pharmaceutically acceptable salt thereof, wherein:

-   -   (a) R₁, R₂ and R₃ are independently selected from the group         consisting of hydrogen, lower alkyl, lower alkoxy, halogen,         hydroxy, (di-lower alkyl)amino, 4-morpholinyl, 1-pyrrolidinyl,         1-pyrrolyl, —CF₃, —OCF₃, phenyl and methoxyphenyl;         -   or R₁ and R₂ together are methylenedioxy;         -   or R₁ and R₂ together with the carbon atoms to which they             are attached form a benzene ring; and     -   (b) R^(a) is hydrogen and R^(b) and R^(c), together with the         carbon atoms to which they are attached, form a saturated ring         of 5 carbons;     -   or R^(a) is lower alkyl, R^(b) is hydrogen or lower alkyl, and         R^(c) is hydrogen; or R^(a), R^(b) and the carbon atom to which         they are attached form a saturated ring of 5-7 carbons, and         R^(c) is hydrogen;     -   or R^(a) is hydrogen, and R^(b), R^(c) and the carbon atoms to         which they are attached form a tetrahydrofuran ring;     -   or R^(a) and R^(b), together with the carbon atom to which they         are attached, and R^(b) and R^(c), together with the carbon         atoms to which they are attached, each form a saturated ring of         5-7 carbons.

In another embodiment of the present invention, the PDE1 inhibitor a compound of Formula XX as follows:

-   -   7.1 Formula XX, wherein R₁, R₂ and R₃ are independently selected         from the group consisting of hydrogen, lower alkyl, lower         alkoxy, halogen, hydroxy, (di-lower alkyl)amino, 4-morpholinyl,         1-pyrrolidinyl, 1-pyrrolyl, —CF₃, —OCF₃, phenyl and         methoxyphenyl; or R₁ and R₂ together are methylenedioxy; or R₁         and R₂ together with the carbon atoms to which they are attached         form a benzene ring;     -   7.2 Formula XX or 7.1, wherein R₁ is H, methoxy or         trifluoromethyl;     -   7.3 Formula XX or 7.1 or 7.2, wherein R₁ is H;     -   7.4 Formula XX or any of 7.1-7.3, wherein R₂ is selected from a         group consisting of H, halo (e.g., F, Cl), methoxy, methyl,         trifluoromethyl, dimethylamino, phenyl, methoxyphenyl-, —OCF₃,         3,4—OCH₂O—, pyrolidin-1-yl, pyrol-1-yl and morpholin-4-yl;     -   7.5 Formula XX or any of 7.1-7.4, wherein R₁ and R₂ together         with the carbon atoms to which they are attached forma a benzene         ring;     -   7.6 Formula XX or any of 7.1-7.5, wherein R₃ is H or methoxy;     -   7.7 Formula XX or any of 7.1-7.6, wherein R₃ is H;     -   7.8 Formula XX or any of 7.1-7.7, wherein R^(a) is hydrogen and         R and R^(c), together with the carbon atoms to which they are         attached, form a saturated ring of 5 carbons; or R^(a) is lower         alkyl, R^(b) is hydrogen or lower alkyl, and R^(c) is hydrogen;         or R^(a), R^(b) and the carbon atom to which they are attached         form a saturated ring of 5-7 carbons, and R^(c) is hydrogen; or         R^(a) is hydrogen, and R^(b), R^(c) and the carbon atoms to         which they are attached form a tetrahydrofuran ring; or R^(a)         and R^(b), together with the carbon atom to which they are         attached, and R^(b) and R^(c), together with the carbon atoms to         which they are attached, each form a saturated ring of 5-7         carbons;     -   7.9 Formula XX or any of 7.1-7.8, wherein R^(a) is hydrogen and         R^(b) and R^(c) together with the carbon atoms to which they are         attached, form a saturated ring of 5 carbons, and wherein R₁, R₂         and R₃ are as defined in the following table

R₁ R₂ R₃ H H H —OCH₃ H H H F H H —OCH₃ H H OH H H —CH₃ H H (CH₂)₂N— H —OCH₃ —OCH₃ —OCH₃ —OCH₃ —OCH₃ H —CF₃ H H H C₆H₃— H H —OCF₃ H H

H H

H 3,4-OCH₂O— H H

H H

H R₁ and R₂, together with the H carbon atoms to which they are attached form a benzene ring H Cl H.

-   -   7.10 Formula XX or any of 7.1-7.9, selected from a group         consisting of:

-   -   7.11 Formula XX or any of 7.1-7.9, selected from a group         consisting of:

-   2¹-benzyl-5′-methyl-spiro[cyclopentane-1′,7′(8′H)-[3′H]-imidazo[2,1-b]purin]-4′-(5′H)-one;

-   2′-benzyl-5,7,7-trimethyl-3H-imidazo[2,1-b]purin-4-(5H)-one;

-   (+)-2-benzyl-7,8-dihydro-5-methyl-7-(1-methylethyl)-1H-imidazo[2,1-b]-purin-4(5H)-one;

-   (+,−)-6a,7,8,9,9a,10,11,11a-octahydro-5-methyl-2-(3,4-methylene-dioxyphenylmethyl)-3H-pentalen[6a,     1:4,5]imidazo[2,1-b]purin-4(5H)-one; and

-   (+)-cis-6a,7,9,9a-tetrahydro-5-methyl-2-[4-(trifluoromethyl)-phenylmethyl]-3H-furo[3′,4′:4,5]imidazo[2,1-b]purin-4(5H)-one,

-   in free or salt form.     -   7.12 Formulae XX or 7.1-7.11, wherein the compounds inhibit         phosphodiesterase-mediated (e.g., PDE1-mediated) hydrolysis of         cGMP, e.g., with an IC₅₀ of less than 1 μM, preferably less than         25 nM.

In another embodiment of the present invention, the PDE1 inhibitor is a compound selected from the following:

in free or salt form (Formula XXI).

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XXII:

wherein,

-   -   R¹ represents a group selected from H, C₁-C₆ alkyl, C₂-C₆         alkenyl, C₂-C₆ alkynyl, cycloalkyl optionally substituted with         one or more of OH, CF₃, CN, halogen or —CONH₂ or C₁-C₆ alkyl;     -   R² represents a group selected from H, C₁-C₆ alkyl, C₂-C₆         alkenyl, C₂-C₆ alkynyl, cycloalkyl optionally substituted with         one or more of OH, CF₃, CN, halogen or —CONH₂ or C₁-C₆ alkyl;     -   R³ represents         -   (i) alkyl (e.g., C₁-C₆ alkyl),         -   (ii) substituted or unsubstituted aryl or substituted or             unsubstituted aralkyl (e.g., (CH₂)_(m)-aryl, wherein the             aryl may be optionally substituted by one or more of halo,             CF₃, OCH₃, heteroaryl, CH₂-heterocycloalkyl containing 2 or             more heteroatoms, N-linked heterocycloalkyl optionally             substituted with one more of C₁-C₄ alkyl, CF₃, halogen, or             heteroaryl), or         -   (iii) substituted or unsubstituted heteroaryl or substituted             or unsubstituted heteroarylalkyl (e.g.,             (CH₂)_(n)-heteroaryl, wherein the heteroaryl may be             optionally substituted by one or more aryl or two or more             C₁-C₄ alkyl); or         -   (iv) aryl optionally substituted by one or more halogen,         -   where each “m” independently represents 0, 1 or 2, and each             “n” independently represents 0 or 1;     -   R⁴ represents H or alkyl (e.g., C₁-C₆ alkyl);     -   or R³ and R⁴ together with the N to which they are attached may         form (i) heterocycloalkyl unsubstituted or substituted with         alkyl, aralkyl, halo substituted aralkyl, heteroarylalkyl or         halo substituted heteroarylalkyl (e.g., where the         heterocycloalkyl is a 4-7 membered N-containing         heterocycloalkyl, optionally substituted with         (CH₂)_(n)-heteroaryl or (CH₂)_(n)-aryl optionally substituted         with one or more halogen, where each “n” is independently 0 or         1); or (ii) 1,2,3,4-tetrahydroisoquinoline;     -   and wherein “aralkyl” or “arylalkyl” refers to a radical in         which an aryl group is substituted for a hydrogen of an alkyl         group; “heteroarylalkyl” refers to a radical in which a         heteroaryl group is substituted for a hydrogen of an alkyl         group; “aryl” refers to a monovalent aromatic hydrocarbon group         derived by the removal of one hydrogen atom from a single carbon         atom of a parent aromatic ring system, and may be monocyclic or         a bicyclic fused ring structure where at least one of the rings         is an aromatic ring structure; “heteroaryl” refers to a         monovalent heteroaromatic group derived by the removal of one         hydrogen atom from a single atom of a parent heteroaromatic ring         system, and may be a monocyclic group or a bicyclic fused ring         structure where at least one of the rings is an aromatic ring         structure and at least one of the rings contains a heteroatom;         “cycloalkyl refers to a cyclic hydrocarbyl group having from 3         to 10 carbon atoms, a single cyclic ring or multiple condensed         rings, including fused or bridged rings, which are optionally         substituted with from 1 to 3 alkyl groups; “heterocycloalkyl”         refers to a stable heterocyclic non-aromatic ring and fused         rings containing one or more heteroatoms; “hetero” as used as a         prefix refers to a structure wherein a carbon atom is replaced         by a nitrogen, oxygen or sulfur atom; “heteroatom” refers to a         nitrogen, oxygen, or sulfur atom; unless otherwise specified,         “substituted” refers to a group in which one or more hydrogen         atoms are each independently replaced with the same or different         substituents (e.g., halogen, alkyl, aryl, heteroaryl, alkoxy,         aryloxy, heteroaryloxy, oxo, hydroxy, thioalkyl, thioaryl,         thioheteroaryl, thiol, thioxo, amino, N-alkylamino,         N,N-dialkylamino, N-arylamino, N,N-diarylamino,         N-heteroarylamino, N,N-diheteroarylamino, N-aryl-N-alkylamino,         N-heteroaryl-N-alkylamino, N-aryl-N-heteroarylamino, haloalkyl,         trifluoromethyl, cyano, azido, carboxy, alkylsulfonyl,         arylsulfonyl, heteroarylsulfonyl, alkylcarbonyl, arylcarbonyl,         heteroarylcarbonyl, esters, amides, sulfonamides, and ureas);         or a pharmaceutically acceptable salt, hydrate, solvate or         prodrug thereof.

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XXII, selected from the following, in free or salt form:

-   5-(4-(2-chloro-6-fluorobenzyl)-1,4-diazepan-1-yl)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((3,4-dichlorobenzyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(4-(piperidin-1-yl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(dipropylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methy     1(3-(trifluoromethyl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(4-(4-methylpiperazin-1-yl)benzylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(1H-indazol-5-ylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(3,4-dihydroisoquinolin-2(1H)-yl)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((4-methoxybenzyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(3-morpholinobenzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(3-(piperidin-1-yl)benzylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(3-(pyrimidin-5-yl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(4-(pyrimidin-5-yl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(((1,5-dimethyl-1H-pyrazol-3-yl)methyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7     (6H)-one; -   5-((3-chlorobenzyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(4-(trifluoromethyl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((4-chlorobenzyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(3-fluorobenzylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(isopentylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((3,4-dimethoxyphenethyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((4-fluorobenzyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(phenethyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin     7(6H)-one; -   5-(4-fluorobenzylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((2-chlorobenzyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl((5-phenylisoxazol-3-yl)methyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-3-propyl-5-(3-(pyrrolidin-1-yl)benzylamino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(4-(morpholinomethyl)benzylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(benzyl(isopropyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(diisobutylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(propyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(3,5-bis(trifluoromethyl)benzylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(3,4-dichlorobenzylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(benzyl(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(6-fluoro-3,4-dihydroisoquinolin-2(1H)-yl)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl((1-methyl-1H-indazol-3-yl)methyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(thieno[2,3-b]pyridin-2-ylmethyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(6,7-dimethoxy-1-methyl-3,4-dihydroisoquinolin-2     (1H)-yl)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl((1-methyl-3-phenyl-1H-pyrazol-5-yl)methyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7     (6H)-one; -   1-methyl-5-(methyl((2-(4-(trifluoromethyl)phenyl)thiazol-4-yl)methyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(4-(pyridin-4-yl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl((2-(pyrrolidin-1-yl)pyridin-4-yl)methyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl((6-morpholinopyridin-2-yl)methyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(3-(pyridin-4-yl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(4-(pyridin-2-yl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((3,4-dichlorobenzyl)(isopentyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(butyl(3,4-dichlorobenzyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl((4-methyl-2-phenylthiazol-5-yl)methyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(3-(2-morpholinoethoxy)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(4-(2-morpholinoethoxy)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(2-(2-morpholinoethoxy)benzylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((5-methyl-3-phenylisoxazol-4-yl)methylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((5-methyl-2-phenyl-2H-1,2,3-triazol-4-yl)methylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(3-(morpholinomethyl)benzylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((2-morpholinopyridin-4-yl)methylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(3-(2-morpholinoethoxy)benzylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(3-morpholinobenzylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((1-phenyl-1H-pyrazol-3-yl)methylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(naphthalen-1-ylmethyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(4-(2,2-diphenylacetoyl)piperazin-1-yl)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-3-propyl-5-(4-(trifluoromethyl)piperidin-1-yl)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(4-morpholinobenzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((2,3-dihydrobenzofuran-5-yl)methylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(1H-pyrazol-1-yl)benzylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(1H-pyrrol-1-yl)benzylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(3-(2-methylthiazol-4-yl)benzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((1-methyl-3-phenyl-1H-pyrazol-5-yl)methylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl-1H-pyrazol-3-yl)benzylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((1-methyl-1H-indol-5-yl)methylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((1-methyl-1H-indol-6-yl)methylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-cyclopentyl-5-((4-fluorobenzyl)(methyl)amino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((4-chlorobenzyl)(methyl)amino)-3-cyclopentyl-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((4-methyl-2-phenylthiazol-5-yl)methylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(1H-1,2,4-triazol-1-yl)benzylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(isobutyl(3-morpholinobenzyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((4-chlorophenethyl)(propyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-cyclopentyl-5-(3,4-dichlorobenzylamino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-cyclopentyl-5-((3,4-dichlorobenzyl)(methyl)amino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-cyclopentyl-5-(dipropylamino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(4-chlorophenethylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-1-methyl-5-(methyl((4-methyl-2-phenylthiazol-5-yl)methyl)amino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-1-methyl-5-(methyl((1-methyl-3-phenyl-1H-pyrazol-5-yl)methyl)amino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(3,4-diethoxyphenethylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-([1,2,4]triazolo[4,3-a]pyridin-3-ylmethylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-cyclopentyl-1-methyl-5-(2-methylpiperidin-1-yl)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-cyclopentyl-1-methyl-5-(piperidin-1-yl)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-cyclopentyl-1-methyl-5-(2-phenylpyrrolidin-1-yl)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(4-fluorophenethylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(2-(1-phenyl-1H-pyrazol-4-yl)ethylamino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-5-(dipropylamino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-1-methyl-5-(methyl(3-(2-methylthiazol-4-yl)benzyl)amino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1-benzyl-3,5-dimethyl-1H-pyrazol-4-yl)methylamino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-1-methyl-5-(3-(4-methylpiperazin-1-yl)benzylamino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-pyrazol-1-yl)benzyl)(isobutyl)amino)-3-tert-butyl-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-pyrazol-1-yl)benzyl)(isobutyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-1,2,4-triazol-1-yl)benzyl)(isobutyl)amino)-3-tert-butyl-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-1,2,4-triazol-1-yl)benzyl)(isobutyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-5-((4-fluorobenzyl)(isobutyl)amino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((4-fluorobenzyl)(isobutyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-5-(isobutyl(methyl)amino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-pyrrol-1-yl)benzyl)(isobutyl)amino)-3-tert-butyl-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-pyrrol-1-yl)benzyl)(isobutyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-(isobutyl(3-(4-methylpiperazin-1-yl)benzyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-5-((3,3-dimethylbutyl)(3-morpholinobenzyl)amino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-1-methyl-5-((2-methylpentyl)(3-morpholinobenzyl)amino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-5-((2-ethylbutyl)(methyl)amino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-pyrazol-1-yl)benzyl)(isopentyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-pyrazol-1-yl)benzyl)(2-ethylbutyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((3,3-dimethylbutyl)(3-morpholinobenzyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-5-((2-ethylbutyl)(3-morpholinobenzyl)amino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((3,3-dimethylbutyl)(methyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-5-((3,3-dimethylbutyl)(methyl)amino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(2-methylbutyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((2-methylpentyl)(3-morpholinobenzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-((2-methylbutyl)(3-morpholinobenzyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-1-methyl-5-(methyl(2-methylpentyl)amino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-1,2,4-triazol-1-yl)benzyl)(2-methylbutyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-1-methyl-5-((2-methylbutyl)(3-morpholinobenzyl)amino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-1,2,4-triazol-1-yl)benzyl)(2-methylbutyl)amino)-3-tert-butyl-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-pyrazol-1-yl)benzyl)(neopentyl)amino)-1-methyl-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   4-((1-methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo[4,3-d]pyrimidin-5-ylamino)methy     1)benzenesulfonamide; -   5-((1H-pyrazol-1-yl)benzyl)(2-ethylbutyl)amino)-3-tert-butyl-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   5-((1H-pyrazol-1-yl)benzyl)(2-methylpentyl)amino)-3-tert-butyl-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   1-methyl-5-(methyl(2-methylpentyl)amino)-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one; -   3-tert-butyl-1-ethyl-5-(isobutyl(3-morpholinobenzyl)amino)-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one;     and -   3-cyclopropyl-5-(dipropylamino)-1-methyl-1H-pyrazolo[4,3-d]pyrimidin-7(6H)-one.

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XXIII:

wherein,

-   -   A represents a bond, —(CH2)n-, —CO, —CONR4-, —CSNR4-,         —C(═N—CN)NR4-, C(═CH—NO2)NR4, —COO—, —SO2-, or —SO2NR4-, aryl or         heteroaryl, optionally substituted with one or more groups     -   selected from halogen, CF₃, C₁-C₆ alkyl, C₁-C₆ alkyl-cycloalkyl,         cycloalkyl, heterocycloalkyl —SO₂R⁴— and C₁-C₆         alkyl-heterocycloalkyl, where A is linked to X via a nitrogen         atom within the X group;     -   B represents bond, C₁-C₆ alkyl, (CH₂)_(m)-cycloalkyl,         —(CH₂)_(m)-heterocycloalkyl, (CH₂)_(m)-aryl or         (CH₂)_(m)-heteroaryl optionally substituted with one or more         groups selected from halogen, CN, CF₃, NR⁴R⁵, NR⁵COR⁴, CONR⁴R⁵,         NR⁵SO₂R⁴, SO₂NR⁴R⁵, C₁-C₆ alkyl, (CH₂)_(n)-heterocycloalkyl         (optionally substituted by C₁-C₆ alkyl), N₂, OR⁴, COR⁴, CO₂R⁴,         or SO₂R⁴     -   X represents a carbon-carbon bonded nitrogen-containing         heterocycloalkyl group;     -   R¹ represents H, C₁-C₆ alkyl, (CH₂)_(n)-aryl, cycloalkyl or         —C₁-C₆ alkyl-cycloalkyl group, each of which may optionally be         substituted with one or more groups selected from halogen, CN,         CF₃, NR⁴R⁵, NHCOR⁴, CONH₂, NHSO₂R⁴, SO₂NHR⁴, C₁-C₆ alkyl, C₁-C₆         alkoxy, COR⁴, CO₂R⁴, or SO₂R₄;     -   R² represents H, C₁-C₆ alkyl, cycloalkyl, heterocycloalkyl,         (CH₂)_(n)-aryl, or a (CH₂)_(n)-heteroaryl group, each of which         may optionally be substituted with one or more groups selected         from halogen, CN, CF₃, NR⁴R⁵, NHCOR⁴, CONH₂, NHSO₂R⁴, SO₂NHR⁴,         SO₂R⁴, C₁-C₆ alkyl, OR⁴, COR⁴, CO₂R⁴, or SO₂R₄;     -   R³ represents H, halogen, C₁-C₆ alkyl, cycloalkyl,         (CH₂)_(n)-aryl, aryl, or a heteroaryl group, each of which may         optionally be substituted with one or more groups selected from         halogen, CN, CF₃, NR⁴R⁵, NHCOR⁴, CONH₂, NHSO₂R⁴, SO₂NHR⁴, SO₂R⁴,         C₁-C₆ alkyl, C₁-C₆ alkoxy, COR⁴, CO₂R⁴, or SO₂R⁴;     -   each R⁴ independently represents H, C₁-C₆ alkyl, cycloalkyl,         heterocycloalkyl, CF₃ or CHF₂;     -   R⁵ represents H, C₁-C₆ alkyl, or cycloalkyl;     -   each “n” independently represents 0,1, 2 or 3;     -   each “m” represents 0, 1, 2, 3, 4, 5 or 6;     -   and wherein the term “aralkyl” or “arylalkyl” refers to a         radical in which an aryl group is substituted for a hydrogen of         an alkyl group; “heteroarylalkyl” refers to a radical in which a         heteroaryl group is substituted for a hydrogen of an alkyl         group; “aryl” refers to a monovalent aromatic hydrocarbon group         derived by the removal of one hydrogen atom from a single carbon         atom of a parent aromatic ring system, and may be monocyclic or         a bicyclic fused ring structure where at least one of the rings         is an aromatic ring structure; “heteroaryl” refers to a         monovalent heteroaromatic group derived by the removal of one         hydrogen atom from a single atom of a parent heteroaromatic ring         system, and may be a monocyclic group or a bicyclic fused ring         structure where at least one of the rings is an aromatic ring         structure and at least one of the rings contains a heteroatom;         “cycloalkyl refers to a cyclic hydrocarbyl group having from 3         to 10 carbon atoms, a single cyclic ring or multiple condensed         rings, including fused or bridged rings, which are optionally         substituted with from 1 to 3 alkyl groups; “heterocycloalkyl”         refers to a stable heterocyclic non-aromatic ring and fused         rings containing one or more heteroatoms; “hetero” as used as a         prefix refers to a structure wherein a carbon atom is replaced         by a nitrogen, oxygen or sulfur atom; “heteroatom” refers to a         nitrogen, oxygen, or sulfur atom; unless otherwise specified,         “substituted” refers to a group in which one or more hydrogen         atoms are each independently replaced with the same or different         substituents (e.g., halogen, alkyl, aryl, heteroaryl, alkoxy,         aryloxy, heteroaryloxy, oxo, hydroxy, thioalkyl, thioaryl,         thioheteroaryl, thiol, thioxo, amino, N-alkylamino,         N,N-dialkylamino, N-arylamino, N,N-diarylamino,         N-heteroarylamino, N,N-diheteroarylamino, N-aryl-N-alkylamino,         N-heteroaryl-N-alkylamino, N-aryl-N-heteroarylamino, haloalkyl,         trifluoromethyl, cyano, azido, carboxy, alkylsulfonyl,         arylsulfonyl, heteroarylsulfonyl, alkylcarbonyl, arylcarbonyl,         heteroarylcarbonyl, esters, amides, sulfonamides, and ureas);         in free form or as a pharmaceutically acceptable salt, hydrate,         solvate or prodrug thereof.

In another embodiment of the present invention, the PDE1 inhibitor is a compound of Formula XXIII selected from:

-   N-(benzo[d][1,3]dioxol-5-yl)-3-(1-tert-butyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-(4-isopropylpiperazin-1-yl)phenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-(4-methylpiperazin-1-yl)phenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(3,4-dimethylphenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(cyclohexylmethyl)azetidine-1-carboxamide; -   3-(1-tert-butyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-phenylazetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(3-(dimethylamino)phenyl)azetidine-1-carboxamide; -   N-(3-chlorophenyl)-3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-(dimethylamino)phenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-morpholinophenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-phenylazetidine-1-carboxamide; -   3-(1-tert-butyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-fluorophenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-methoxyphenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-phenylazetidine-1-carboxamide; -   3-(1-tert-butyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-cyclohexylazetidine-1-carboxamide; -   3-(1-tert-butyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-fluorophenyl)azetidine-1-carboxamide; -   3-(1-tert-butyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-fluorobenzyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-isopropylphenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-fluorophenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(3,4-difluorophenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-fluorophenyl)azetidine-1-carboxamide; -   N-benzyl-3-(1-tert-butyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   N-cyclohexyl-3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   N-benzyl-3-(1-cyclohexyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-(trifluoromethoxy)phenyl)azetidine-1-carboxamide; -   tert-butyl     3-(3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamido)piperidine-1-carboxylate; -   3-(1-cyclohexyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-fluorobenzyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-methoxybenzyl)azetidine-1-carboxamide; -   N-(2-(difluoromethoxy)phenyl)-3-(1-(4-fluorophenyl)-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-fluorobenzyl)azetidine-1-carboxamide; -   N-benzyl-3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-cyclopentylazetidine-1-carboxamide; -   N-(4-cyanophenyl)-3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   N-butyl-3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-(trifluoromethyl)phenyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(3,4-dichlorobenzyl)azetidine-1-carboxamide; -   N-tert-butyl-3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(3,4-dichlorobenzyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(1-(methylsulfonyl)piperidin-4-yl)azetidine-1-carboxamide; -   tert-butyl     4-(3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxamido)piperidine-1-carboxylate; -   (S)-3-(1-cyclohexyl-3-methyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(1-phenylethyl)azetidine-1-carboxamide; -   3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(3,3,3-trifluoropropyl)azetidine-1-carboxamide; -   1-cyclohexyl-6-(1-(3,4-dimethoxyphenylsulfonyl)piperidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   4-(4-isopropylpiperazin-1-yl)phenyl     3-(1-tert-butyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxylate; -   cyclohexylmethyl     3-(1-tert-butyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxylate; -   3-chlorophenyl     3-(1-tert-butyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxylate; -   benzo[d][1,3]dioxol-5-yl     3-(1-tert-butyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxylate; -   cyclohexylmethyl     3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxylate; -   4-fluorophenyl     3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidine-1-carboxylate; -   6-(1-(1H-benzo[d]imidazol-2-yl)azetidin-3-yl)-1-cyclohexyl-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   6-(1-(6-bromo-1H-benzo[d]imidazol-2-yl)azetidin-3-yl)-1-tert-butyl-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-tert-butyl-6-(1-(5-(trifluoromethyl)-1H-benzo[d]imidazol-2-yl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   6-(1-(1H-benzo[d]imidazol-2-yl)azetidin-3-yl)-1-tert-butyl-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-cyclohexyl-6-(1-(4-phenyloxazol-2-yl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-cyclohexyl-6-(1-(4-(morpholinosulfonyl)phenyl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   6-(1-(3-amino-4-nitrophenyl)azetidin-3-yl)-1-cyclohexyl-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   6-(1-(4-acetylphenyl)azetidin-3-yl)-1-cyclohexyl-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   4-(3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)azetidin-1-yl)benzonitrile; -   1-cyclohexyl-6-(1-(3-methyl-4-nitrophenyl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-cyclohexyl-6-(1-(4-(morpholinomethyl)phenyl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-cyclohexyl-6-(1-(5-phenyl-4H-1,2,4-triazol-3-yl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-cyclohexyl-6-(1-(4-phenylthiazol-2-yl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-cyclohexyl-6-(1-(4-(4-(4-isopropylpiperazin-1-yl)phenyl)thiazol-2-yl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-cyclohexyl-6-(1-(5-(morpholinomethyl)-4-phenylthiazol-2-yl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   1-tert-butyl-6-(1-(4-(morpholinomethyl)phenyl)azetidin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one; -   (Z)—N′-cyano-3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(4-fluorophenyl)azetidine-1-carboximidamide; -   (Z)—N′-cyano-3-(1-cyclohexyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N-(cyclohexylmethyl)azetidine-1-carboximidamide;     and -   (Z)-3-(1-tert-butyl-4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-6-yl)-N′-cyano-N-(4-fluorophenyl)azetidine-1-carboximidamide;     or a pharmaceutically acceptable salts thereof.     NEP Inhibitors

In one embodiment, the NEP inhibitors for use in the current invention are selective NEP inhibitors. In a further embodiment, the NEP inhibitors for use in the current invention are inhibitors with at least 300-fold selectivity for NEP inhibition over ACE inhibition. In a further embodiment, the NEP inhibitors for use in the current invention are inhibitors with at least 100-fold selectivity for NEP inhibition over ECE (Endothelin Converting Enzyme) inhibition. In yet another embodiment, the NEP inhibitors for use in the current invention are inhibitors with at least 300-fold selectivity for NEP inhibition over ACE inhibition and 100-fold selectivity for NEP inhibition over ECE inhibition.

In another embodiment, the NEP inhibitors for use in the current invention are the NEP inhibitors disclosed in the following patents, patent applications or non-patent publications: EP-1097719 B1, EP-509442A, U.S. Pat. No. 4,929,641, EP-599444B, US-798684, J. Med. Chem. (1993) 3821, EP-136883, U.S. Pat. No. 4,722,810, Curr. Pharm. Design (1996) 443, J. Med. Chem. (1993) 87, EP-830863, EP-733642, WO 9614293, WO 9415908, WO 9309101, WO 9109840, EP-519738, EP-690070, Bioorg. Med. Chem. Lett. (1996) 65, EP-A-0274234, Biochem. Biophys. Res. Comm. (1989) 58, Perspect. Med. Chem. (1993) 45, or EP-358398-B. The contents of these patents and publications are hereby incorporated by reference in their entirety herein. In another embodiment, the NEP inhibitors for use in the current invention are the NEP inhibitors Phosphoramidon, Thiorphan, Candoxatrilat, Candoxatril, or the compound of the Chemical Abstract Service (CAS) Number 115406-23-0.

In another embodiment, the NEP inhibitors for use in the current invention are the NEP inhibitors disclosed in US 2006/0041014 A1, the contents of which are hereby incorporated by reference in their entirety herein.

In another embodiment, the NEP inhibitors for use in the current invention are the NEP inhibitors disclosed in U.S. Pat. No. 5,217,996, the contents of which are hereby incorporated by reference in their entirety herein.

In another embodiment, the NEP inhibitors for use in the current invention are the NEP inhibitors disclosed in U.S. Pat. No. 8,513,244, the contents of which are hereby incorporated by reference in their entirety herein.

In another embodiment, the NEP inhibitors for use in the current invention are the NEP inhibitors disclosed in U.S. Pat. No. 5,217,996, the contents of which are hereby incorporated by reference in their entirety herein.

In another embodiment, the NEP inhibitors for use in the current invention are the NEP inhibitors disclosed in US patent application publication 2013/0330365, the contents of which are hereby incorporated by reference in their entirety herein.

In another embodiment, the NEP inhibitor for use in the current invention is 3-[{1S, 3R}-1-biphenyl-4-ylmethyl-3-ethoxycarbonyl-1-butylcarbamoyl]propionic acid,

also known as AHU-377, or a pharmaceutically acceptable salt or prodrug, thereof, and in a preferred embodiment thereof, the sodium salt.

In another embodiment, the NEP inhibitor for use in the current invention is 3-[{1S, 3R}-1-biphenyl-4ylmethyl-3-carboxy-1-butylcarbamoyl]propionic acid,

also known as LBQ-657, or any pharmaceutically acceptable ester, salt or prodrug thereof.

In another embodiment, the NEP inhibitor for use in the current invention is selected from among the following, in free or pharmaceutically acceptable salt form or in prodrug form thereof: sampatrilat, fasidotril, Z13752A, MDL 100240, BMS 189921, LBQ657, AHU-377, or mixanpril, in free or pharmaceutically acceptable salt form or in prodrug form thereof.

In another embodiment, the NEP inhibitor for use in the current invention is selected from among the following, in free or pharmaceutically acceptable salt form or in prodrug form thereof:

SQ 28,603;

N-[N-[((1S)-carboxy-3-phenylpropyl]-(S)-phenylalanyl]-S-isoserine;

N-[N-[((1S)-carboxy-2-phenyl)ethyl]-(S)-phenylalanyl]-beta-alanine;

N-[(2S)-mercaptomethyl-3-(2-methylphenyl)-propionyl]methionine;

(cis-4-[[[1-[2-carboxy-3-(2-methoxy-ethoxy)propyl]-cyclopentyl]carbonyl]amino]cyclohexanecarboxylic acid);

thiorphan; retro-thiorphan; phosphoramidon; SQ 29072;

N-(3-carboxy-1-oxopropyl)-(4S)-p-phenylphenylmethyl)-4-amino-2R-methylbutanoic acid ethyl ester;

(S)-cis-4-[1-[2-(5-indanyloxycarbonyl)-3-(2-methoxyethoxy)propyl]-1-cyclopentanecarboxamido]-1-cyclohexanecarboxylic acid;

3-(1-[6-endo-hydroxymethylbicyclo[2,2,1]heptane-2-exo-carbamoyl]cyclopentyl)-2-(2-methoxyethyl)propanoic acid;

N-(1-(3-(N-t-butoxycarbonyl-(S)-prolylamino)-2(S)-t-butoxy-carbonylpropyl) cyclopentanecarbonyl)-O-benzyl-(S)-serine methyl ester;

4-[[2-(mercaptomethyl)-1-oxo-3-phenylpropyl]amino]benzoic acid;

3-[1-(cis-4-carboxycarbonyl-cis-3-butylcyclohexyl-r-1-carbamoyl)cyclopentyl]-2S-(2-methoxyethoxymethyl)propanoic acid;

N-((2S)-2-(4-biphenylmethyl)-4-carboxy-5-phenoxyvaleryl)glycine;

N-(1-(N-hydroxycarbamoylmethyl)-1-cyclopentanecarbonyl)-L-phenylalanine;

(S)-(2-biphenyl-4-yl)-1-(1H-tetrazol-5-yl)ethylamino)methylphosphonic acid;

(S)-5-(N-(2-(phosphonomethylamino)-3-(4-biphenyl)propionyl)-2-aminoethyl)tetrazole; beta-alanine;

3-[1,1′-biphenyl]-4-yl-N-[diphenoxyphosphinyl)methyl]-L-alanyl;

N-(2-carboxy-4-thienyl)-3-mercapto-2-benzylpropanamide;

2-(2-mercaptomethyl-3-phenylpropionamido)thiazol-4-ylcarboxylic acid;

(L)-(1-((2,2-dimethyl-1,3-dioxolan-4-yl)methoxy)carbonyl)-2-phenylethyl)-L-phenylalanyl)-beta-alanine;

N-[N-[(L)-[1-[(2,2-dimethyl-1,3-dioxolan-4-yl)-methoxy]carbonyl]-2-phenylethyl]-L-phenylalanyl]-(R)- alanine;

N-[N-[(L)-1-carboxy-2-phenylethyl]-Lphenylalanyl]-(R)-alanine;

N-[2-acetylthiomethyl-3-(2-methyl-phenyl)propionyl]-methionine ethyl ester;

N-[2-mercaptomethyl-3-(2-methylphenyl)propionyl]-methionine;

N-[(2S)-mercaptomethyl-3-(2-methylphenyl)propanoyl]-(S)-isoserine;

N-(S)-[3-mercapto-2-(2-methylphenyl)propionyl]-(S)-2-methoxy-(R)-alanine;

N-[1-[[(1S)-benzyloxy-carbony 1-3-phenylpropyl] amino] cyclopentylcarbonyl]-(S) isoserine;

N-[1-[[(1S)-carbonyl-3-phenylpropyl]amino]cyclopentylcarbonyl]-(S)-isoserine;

1,1′-[dithiobis-[(2S)-(2-methylbenzyl)-1-oxo-3, 1-propanediyl]]-bis-(S)-isoserine;

1,1′-[dithiobis-[(2S)-(2-methylbenzyl)-1-oxo-3, 1-propanediyl]]-bis-(S)-methionine;

N-(3-phenyl-2-(mercaptomethyl)-propionyl)-(S)-4-(methylmercapto)methionine;

N-[2-acetylthiomethyl-3-phenyl-propionyl]-3-aminobenzoic acid;

N-[2-mercaptomethyl-3-phenyl-propionyl]-3-aminobenzoic acid;

N-[1-(2-carboxy-4-phenylbutyl)-cyclopentane-carbonyl]-(S)-isoserine;

N-[1-(acetylthiomethyl)cyclopentane-carbonyl]-(S)-methionine ethyl ester;

3(S)-[2-(acetylthiomethyl)-3-phenyl-propionyl]amino-epsilon-caprolactam;

N-(2-acetylthiomethyl-3-(2-methylphenyl)propionyl)-methionine ethyl ester.

If not otherwise specified or clear from context, the following terms herein have the following meanings:

-   -   (a) “Selective PDE1 inhibitor” as used herein refers to a PDE1         inhibitor with at least 100-fold selectivity for PDE1 inhibition         over inhibition of any other PDE isoform.     -   (b) “Selective NEP inhibitor” as used herein refers to an NEP         inhibitor with at least 100-fold selectivity for NEP inhibition         over ACE inhibition.     -   (c) “Alkyl” as used herein is a saturated or unsaturated         hydrocarbon moiety, preferably saturated, preferably having one         to six carbon atoms, which may be linear or branched, and may be         optionally mono-, di- or tri-substituted, e.g., with halogen         (e.g., chloro or fluoro), hydroxy, or carboxy.     -   (d) “Cycloalkyl” as used herein is a saturated or unsaturated         nonaromatic hydrocarbon moiety, preferably saturated, preferably         comprising three to nine carbon atoms, at least some of which         form a nonaromatic mono- or bicyclic, or bridged cyclic         structure, and which may be optionally substituted, e.g., with         halogen (e.g., chloro or fluoro), hydroxy, or carboxy. Wherein         the cycloalkyl optionally contains one or more atoms selected         from N and O and/or S, said cycloalkyl may also be a         heterocycloalkyl.     -   (e) “Heterocycloalkyl” is, unless otherwise indicated, saturated         or unsaturated nonaromatic hydrocarbon moiety, preferably         saturated, preferably comprising three to nine carbon atoms, at         least some of which form a nonaromatic mono- or bicyclic, or         bridged cyclic structure, wherein at least one carbon atom is         replaced with N, O or S, which heterocycloalkyl may be         optionally substituted, e.g., with halogen (e.g., chloro or         fluoro), hydroxy, or carboxy.     -   (f) “Aryl” as used herein is a mono or bicyclic aromatic         hydrocarbon, preferably phenyl, optionally substituted, e.g.,         with alkyl (e.g., methyl), halogen (e.g., chloro or fluoro),         haloalkyl (e.g., trifluoromethyl), hydroxy, carboxy, or an         additional aryl or heteroaryl (e.g., biphenyl or pyridylphenyl).     -   (g) “Heteroaryl” as used herein is an aromatic moiety wherein         one or more of the atoms making up the aromatic ring is sulfur         or nitrogen rather than carbon, e.g., pyridyl or thiadiazolyl,         which may be optionally substituted, e.g., with alkyl, halogen,         haloalkyl, hydroxy or carboxy.

Compounds of the Invention, e.g., PDE1 inhibitors and NEP inhibitors as described herein, may exist in free or salt form, e.g., as acid addition salts. In this specification unless otherwise indicated, language such as “Compounds of the Invention” is to be understood as embracing the compounds in any form, for example free or acid addition salt form, or where the compounds contain acidic substituents, in base addition salt form. The Compounds of the Invention are intended for use as pharmaceuticals, therefore pharmaceutically acceptable salts are preferred. Salts which are unsuitable for pharmaceutical uses may be useful, for example, for the isolation or purification of free Compounds of the Invention or their pharmaceutically acceptable salts, are therefore also included.

Compounds of the Invention may in some cases also exist in prodrug form. A prodrug form is compound which converts in the body to a Compound of the Invention. For example when the Compounds of the Invention contain hydroxy or carboxy substituents, these substituents may form physiologically hydrolysable and acceptable esters. As used herein, “physiologically hydrolysable and acceptable ester” means esters of Compounds of the Invention which are hydrolysable under physiological conditions to yield acids (in the case of Compounds of the Invention which have hydroxy substituents) or alcohols (in the case of Compounds of the Invention which have carboxy substituents) which are themselves physiologically tolerable at doses to be administered. Therefore, wherein the Compound of the Invention contains a hydroxy group, for example, Compound-OH, the acyl ester prodrug of such compound, i.e., Compound-O—C(O)—C₁₋₄alkyl, can hydrolyze in the body to form physiologically hydrolysable alcohol (Compound-OH) on the one hand and acid on the other (e.g., HOC(O)—C₁₋₄alkyl). Alternatively, wherein the Compound of the Invention contains a carboxylic acid, for example, Compound-C(O)OH, the acid ester prodrug of such compound, Compound-C(O)O—C₁₋₄alkyl can hydrolyze to form Compound-C(O)OH and HO—C₁₋₄ alkyl. As will be appreciated the term thus embraces conventional pharmaceutical prodrug forms.

In another embodiment, the invention further provides a pharmaceutical composition comprising a PDE1 inhibitor in combination with an NEP inhibitor, each in free or pharmaceutically acceptable salt form, in admixture with a pharmaceutically acceptable carrier. The term “combination”, as used herein, embraces simultaneous, sequential, or contemporaneous administration of the PDE1 inhibitor and the NEP inhibitor. In another embodiment, the invention provides a pharmaceutically composition comprising a PDE1 inhibitor in non-covalent association or complex with an NEP inhibitor. For example, wherein a PDE1 inhibitor containing a basic nitrogen is formed into an acid-base salt with an NEP inhibitor containing an acidic proton. In still another embodiment, the invention provides a compound wherein a PDE1 inhibitor is reversibly covalently bound to an NEP inhibitor. For example, wherein a PDE1 inhibitor containing a free hydroxy group is esterified to the free carboxylic acid of an NEP inhibitor, which resulting ester compound is a pro-drug of both the PDE1 inhibitor and the NEP inhibitor. In another embodiment, the invention provides a pharmaceutical composition containing such a compound. In some embodiments, the combination of the PDE1 inhibitor and the NEP inhibitor allows each to be administered in a dosage lower than would be effective for either agent administered as sole monotherapy.

Methods of Making Compounds of the Invention

The PDE1 inhibitors of the Invention of Formulas I to XI and their pharmaceutically acceptable salts may be made using the methods as described and exemplified in U.S. Pat. No. 8,273,750, US 2006/0173878, U.S. Pat. No. 8,273,751, US 2010/0273753, U.S. Pat. Nos. 8,697,710, 8,664,207, 8,633,180, 8,536,159, US 2012/0136013, US 2011/0281832, US 2013/0085123, US 2013/0324565, US 2013/0338124, US 2013/0331363, WO 2012/171016, and WO 2013/192556, and by methods similar thereto and by methods known in the chemical art. Such methods include, but not limited to, those described below. If not commercially available, starting materials for these processes may be made by procedures, which are selected from the chemical art using techniques which are similar or analogous to the synthesis of known compounds.

The PDE1 inhibitors of the invention of Formulas XV to XXI and their pharmaceutically acceptable salts, and novel intermediates for the preparation thereof, may be made using the methods as described and exemplified in EP 0201188 (or U.S. Pat. No. 4,666,908) and EP 091 1333 (or U.S. Pat. No. 6,235,742); PCT/US2006/022066; PCT/US2006/033179; WO 03/042216 (U.S. Pat. No. 6,943,171); U.S. Pat. Nos. 6,969,719; 5,939,419; EP 0 538 332 (U.S. Pat. No. 5,393,755); Xia et al., J Med. Chem. (1997), 40, 4372-4377 and Ahn et al., J Med. Chem. (1997), 40, 2196-2210, US 2008/0242661, WO 2008/055959, and US 2009/0137549, the contents of each of which are incorporated herein by reference by their entirety.

Various PDE1 inhibitors and starting materials therefor may be prepared using methods described in US 2008-0188492 A1, US 2010-0173878 A1, US 2010-0273754 A1, US 2010-0273753 A1, WO 2010/065153, WO 2010/065151, WO 2010/065151, WO 2010/065149, WO 2010/065147, WO 2010/065152, WO 2011/153129, WO 2011/133224, WO 2011/153135, WO 2011/153136, WO 2011/153138. All references cited herein are hereby incorporated by reference in their entirety.

The NEP inhibitors of the Invention and their pharmaceutically acceptable salts may be made using the methods as described and exemplified herein and by methods similar thereto and by methods known in the chemical art. Such methods include, but not limited to, those described below. If not commercially available, starting materials for these processes may be made by procedures, which are selected from the chemical art using techniques which are similar or analogous to the synthesis of known compounds.

Various NEP inhibitors and starting materials therefor may be prepared using methods described in US 2006-0041014 A1, EP 1097719 A1, U.S. Pat. No. 8,513,244, and US 2013-0330365 A1. All references cited herein are hereby incorporated by reference in their entirety.

The Compounds of the Invention include their enantiomers, diastereomers and racemates, as well as their polymorphs, hydrates, solvates and complexes. Some individual compounds within the scope of this invention may contain double bonds. Representations of double bonds in this invention are meant to include both the E and the Z isomer of the double bond. In addition, some compounds within the scope of this invention may contain one or more asymmetric centers. This invention includes the use of any of the optically pure stereoisomers as well as any combination of stereoisomers.

It is also intended that the Compounds of the Invention encompass their stable and unstable isotopes. Stable isotopes are nonradioactive isotopes which contain one additional neutron compared to the abundant nuclides of the same species (i.e., element). It is expected that the activity of compounds comprising such isotopes would be retained, and such compound would also have utility for measuring pharmacokinetics of the non-isotopic analogs. For example, the hydrogen atom at a certain position on the Compounds of the Invention may be replaced with deuterium (a stable isotope which is non-radioactive). Examples of known stable isotopes include, but not limited to, deuterium, ¹³C, ¹⁵N, ¹⁸O. Alternatively, unstable isotopes, which are radioactive isotopes which contain additional neutrons compared to the abundant nuclides of the same species (i.e., element), e.g., ¹²³I, ¹³¹I, ¹²⁵I, ¹¹C, ¹⁸F, may replace the corresponding abundant species of I, C and F. Another example of useful isotope of the compound of the invention is the ¹¹C isotope. These radio isotopes are useful for radio-imaging and/or pharmacokinetic studies of the compounds of the invention.

Melting points are uncorrected and (dec) indicates decomposition. Temperature are given in degrees Celsius (° C.); unless otherwise stated, operations are carried out at room or ambient temperature, that is, at a temperature in the range of 18-25° C. Chromatography means flash chromatography on silica gel; thin layer chromatography (TLC) is carried out on silica gel plates. NMR data is in the delta values of major diagnostic protons, given in parts per million (ppm) relative to tetramethylsilane (TMS) as an internal standard. Conventional abbreviations for signal shape are used. Coupling constants (J) are given in Hz. For mass spectra (MS), the lowest mass major ion is reported for molecules where isotope splitting results in multiple mass spectral peaks Solvent mixture compositions are given as volume percentages or volume ratios. In cases where the NMR spectra are complex, only diagnostic signals are reported.

Methods of Using Compounds of the Invention

The Compounds of the Invention are useful in the treatment of cardiovascular diseases characterized by increased to cGMP/PKG mediated pathways, e.g., as a result of increased expression of PDE1 or decreased expression of cGMP/PKG activity due to inhibition or reduced levels of inducers of cyclic nucleotide synthesis, such as dopamine and nitric oxide (NO). It is believed that by inhibiting PDE1A, PDE1B and/or PDE1C, for example, that this action could reverse or prevent the attenuation of cGMP/PKG signaling (e.g., enhance cGMP) and that this action could modulate cardiac hypertrophy. Therefore, administration of a preferred PDE1 inhibitor as described herein, e.g., a PDE1 inhibitor as hereinbefore described, e.g., a Compound of Formula Ia, Ib, IIa, IIb, III, IV, V, VI, VII, VIII, IX, X, XI, could provide a potential means to regulate cardiac hypertrophy (e.g., prevent and/or reverse cardiac hypertrophy), and in certain embodiments provide a treatment for various cardiovascular diseases and disorders.

Diseases and disorders that may be prevented or ameliorated by the enhancement of cGMP/PKG signaling (e.g., cardiovascular disease) include, but are not limited to: angina, stroke, renal failure, essential hypertension, pulmonary hypertension, secondary hypertension, isolated systolic hypertension, hypertension associated with diabetes, hypertension associated with atherosclerosis, renovascular hypertension, congestive heart failure, myocardial infarction, hypertension and cardiac hypertrophy.

In another embodiment, the invention further provides for the treatment or prevention of cardiovascular disease or disorder associated with: Duchenne muscular dystrophy, Becker muscular dystrophy, limb-girdle muscular dystrophy, myotonic dystrophy, and Emery-Dreifuss muscular dystrophy. In one embodiment, the Compounds of the Invention are useful in treating cardiac dysfunction associated with aforementioned types of muscular dystrophy. In another embodiment, the Compounds of the Invention may potentially reduce or reverse the cardiac hypertrophy that may be associated with these aforementioned types of muscular dystrophy.

The phrase “Compounds of the Invention” refers to the combination of a PDE1 inhibitor and an NEP inhibitor as each is described herein.

The words “treatment” and “treating” are to be understood accordingly as embracing treatment or amelioration of symptoms of disease as well as treatment of the cause of the disease.

For methods of treatment, the word “effective amount” is intended to encompass a therapeutically effective amount to treat a specific disease or disorder.

The term “patient” include human or non-human (i.e., animal) patient. In particular embodiment, the invention encompasses both human and nonhuman. In another embodiment, the invention encompasses nonhuman. In other embodiment, the term encompasses human.

The term “comprising” as used in this disclosure is intended to be open-ended and does not exclude additional, un-recited elements or method steps.

Dosages employed in practicing the present invention will of course vary depending, e.g. on the particular disease or condition to be treated, the particular Compounds of the Invention used, the mode of administration, and the therapy desired. Compounds of the Invention may be administered by any suitable route, including orally, parenterally, transdermally, or by inhalation, but are preferably administered orally. In general, satisfactory results, e.g. for the treatment of diseases as hereinbefore set forth are indicated to be obtained on oral administration at dosages of the order from about 0.01 to 2.0 mg/kg. In larger mammals, for example humans, an indicated daily dosage for oral administration of both the PDE1 inhibitor and the NEP inhibitor will accordingly be in the range of from about 0.50 to 300 mg, conveniently administered once, or in divided doses 2 to 4 times, daily or in sustained release form. Unit dosage forms for oral administration thus for example may comprise from about 0.2 to 150 or 300 mg, e.g. from about 0.2 or 2.0 to 10, 25, 50, 75 100, 150, or 200 mg of a Compound of the Invention, together with a pharmaceutically acceptable diluent or carrier therefor.

Compounds of the Invention may be administered by any satisfactory route, including orally, parenterally (intravenously, intramuscular or subcutaneous) or transdermally, but are preferably administered orally. In certain embodiments, the Compounds of the Invention, e.g., in depot formulation, is preferably administered parenterally, e.g., by injection.

The Compounds of the Invention and the Pharmaceutical Compositions of the Invention of the Invention may be used in combination with one or more additional therapeutic agents, particularly at lower dosages than when the individual agents are used as a monotherapy so as to enhance the therapeutic activities of the combined agents without causing the undesirable side effects commonly occur in conventional monotherapy. Therefore, the Compounds of the Invention may be simultaneously, separately, sequentially, or contemporaneously administered with other agents useful in treating disease. In another example, side effects may be reduced or minimized by administering a Compound of the Invention in combination with one or more additional therapeutic agents in free or salt form, wherein the dosages of (i) the second therapeutic agent(s) or (ii) both Compound of the Invention and the second therapeutic agent, are lower than if the agent/compound are administered as a monotherapy. By way of non-limiting example, such additional therapeutic agents may include ACE inhibitors, Angiotensin II receptor antagonists, calcium channel blockers, etc.

The term “simultaneously” when referring to a therapeutic use means administration of two or more active ingredients at or about the same time by the same route of administration.

The term “separately” when referring to a therapeutic use means administration of two or more active ingredients at or about the same time by different route of administration.

Pharmaceutical compositions comprising Compounds of the Invention may be prepared using conventional diluents or excipients and techniques known in the galenic art. Thus oral dosage forms may include tablets, capsules, solutions, suspensions and the like.

EXAMPLES Example 1: Measurement of PDEI Inhibition In Vitro Using IMAP Phosphodiesterase Assay Kit

Phosphodiesterase I (including PDE1A, PDEIB and PDE1C) is a calcium/calmodulin dependent phosphodiesterase enzyme that converts cyclic guanosine monophosphate (cGMP) to 5′-guanosine monophosphate (5′-GMP). PDEI can also convert a modified cGMP substrate, such as the fluorescent molecule cGMP-fluorescein, to the corresponding GMP-fluorescein. The generation of GMP-fluorescein from cGMP-fluorescein can be quantitated, using, for example, the IMAP (Molecular Devices, Sunnyvale, Calif.) immobilized-metal affinity particle reagent.

Briefly, the IMAP reagent binds with high affinity to the free 5′-phosphate that is found in GMP-fluorescein and not in cGMP-fluorescein. The resulting GMP-fluorescein—IMAP complex is large relative to cGMP-fluorescein. Small fluorophores that are bound up in a large, slowly tumbling, complex can be distinguished from unbound fluorophores, because the photons emitted as they fluoresce retain the same polarity as the photons used to excite the fluorescence.

In the phosphodiesterase assay, cGMP-fluorescein, which cannot be bound to IMAP, and therefore retains little fluorescence polarization, is converted to GMP-fluorescein, which, when bound to IMAP, yields a large increase in fluorescence polarization (Δmp). Inhibition of phosphodiesterase, therefore, is detected as a decrease in Δmp.

Phosphodiesterase Enzyme Inhibition Assay

Materials: All chemicals are available from Sigma-Aldrich (St. Louis, Mo.) except for IMAP reagents (reaction buffer, binding buffer, FL-GMP and IMAP beads), which are available from Molecular Devices (Sunnyvale, Calif.). Assay: Phosphodiesterase enzymes that may be used include: 3′,5′-cyclic-nucleotide-specific bovine brain phosphodiesterase (Sigma, St. Louis, Mo.) (predominantly PDE1B, but also containing PDE1A and 1C) and recombinant full length human PDE1 A, PDE1B and PDE1B which may be produced e.g., in HEK or SF9 cells by one skilled in the art. The PDE1 enzyme is reconstituted with 50% glycerol to 2.5 U/ml. One unit of enzyme will hydrolyze 1.0 μmol of 3′,5′-cAMP to 5′-AMP per min at pH 7.5 at 30° C. One part enzyme is added to 1999 parts reaction buffer (30 μM CaCl₂, 10 U/ml of calmodulin (Sigma P2277), 10 mM Tris-HCl pH 7.2, 10 mM MgCl₂, 0.1% BSA, 0.05% NaN₃) to yield a final concentration of 1.25 mU/ml. 99 μl of diluted enzyme solution is added into each well in a flat bottom 96-well polystyrene plate to which 1 μl of test compound dissolved in 100% DMSO is added. The compounds are mixed and pre-incubated with the enzyme for 10 min at room temperature. [0084] The FL-GMP conversion reaction is initiated by combining 4 parts enzyme and inhibitor mix with 1 part substrate solution (0.225 μM) in a 384-well microtiter plate. The reaction is incubated in dark at room temperature for 15 min. The reaction is halted by addition of 60 μl of binding reagent (1:400 dilution of IMAP beads in binding buffer supplemented with 1:1800 dilution of antifoam) to each well of the 384-well plate. The plate is incubated at room temperature for 1 hour to allow IMAP binding to proceed to completion, and then placed in an Envision multimode microplate reader (PerkinElmer, Shelton, Conn.) to measure the fluorescence polarization (Δmp).

A decrease in GMP concentration, measured as decreased Δmp, is indicative of inhibition of PDE activity. IC₅₀ values are determined by measuring enzyme activity in the presence of 8 to 16 concentrations of compound ranging from 0.0037 nM to 80,000 nM and then plotting drug concentration versus Δmp, which allows IC₅₀ values to be estimated using nonlinear regression software (XLFit; IDBS, Cambridge, Mass.).

The PDE1 inhibitory activity of Compounds of the Invention are tested in an assay as described or similarly described herein for PDE1 inhibitory activity. For example, the PDE1 inhibitor disclosed in U.S. Pat. No. 8,273,751 on Column 23, line 29-38, has a PDE1A IC₅₀ value of 0.70 nM.

Example 2: Neutral Endopeptidase Enzyme Inhibition Assay

Recombinant human NEP can be obtained commercially from, for example, R&D Systems, Minneapolis, Minn. (Catalog number 1182-ZN). The fluorogenic peptide substrate Mca-D-Arg-Arg-Leu-Dap-(Dnp)-OH (Medeiros et al. (1997) Braz. J. Med. Biol. Res. 30:1157-62; Anaspec, San Jose, Calif.) can be used in the NEP assay. The assay can be performed in a 384-well white opaque plate at 37° C. using the fluorogenic peptide substrate at a concentration of 10 μM in Assay Buffer (50 mM HEPES, pH 7.5, 100 mM NaCl, 0.01% polyethylene glycol sorbitan monolaurate (Tween 20), 10 μM zinc sulfate. The enzyme can be used in a concentration that results in quantitative proteolysis of 1 μM of substrate after 20 minutes at 37° C. Test compounds can be assayed over the range of concentrations from 10 μM to 20 μM. Test compounds are added to the enzyme and incubated for 30 minutes at 37° C. prior to initiating the reaction by the addition of substrate. Reactions are terminated after 20 minutes incubation at 37° C. by the addition of glacial acetic acid to a final concentration of 3.6% v/v. Plates are then read on a fluorometer with excitation and emission wavelengths set to 320 nm and 405 nm, respectively. Inhibition constants can be obtained by nonlinear regression of the data using the equation v=v₀/[1+I/K′)], where v is the reaction rate, v₀ is the uninhibited reaction rate, I is the inhibitor concentration and K′ is the apparent inhibition constant.

Example 3: Human Cardiomyocyte Cellular Screening Assay Method for PDE1

The following screening assay is used to measure the potency of inhibitors of PDE1 in intact cells using a human cardiomyocyte (hCM) cell line developed by Promocell (Heidelberg, Germany). Promocell has devised a proprietary method for the isolation of cardiomyocytes from donated human cardiac tissue. Levels of cGMP can be measured using a competitive enzyme immunoassay (EIA) based system. Acetylcholinesterase-linked cGMP molecules compete with tissue derived cGMP for binding to cGMP-specific antibodies. The amount of antibody bound and acetylcholinesterase-linked cGMP that remains attached to an IgG-coated plate is measured by the acetylcholinesterase activity level. Specifically, acetylthiocholine is converted to thiocholine by the acetylcholinesterase enzyme, and the thiocholine then reacts with the detection reagent 2-nitrobenzoic acid to form 5-thio-2-nitrobenzoic acid, which is yellow. The 412 nm yellow wavelength can be detected and quantified spectrophotometrically.

Inhibition of PDE1 under conditions that stimulate cGMP production cause a further increase of cGMP production. Atrial natriuretic peptide (ANP) causes cGMP production via binding to the natriuretic peptide receptor A (NPRA) which activates the receptor's guanylyl cyclase domain. The Promocell hCMs respond to ANP in a dose dependent manner as measured by intracellular cGMP rise. PDE1 inhibition is found to augment this ANP-induced rise in cGMP, whereas PDE1 inhibition has little effect on basal cGMP levels (in the absence of ANP stimulation). This method has been adapted by Applicants to develop a cell-based assay for testing the potency of PDE1 inhibitors

The hCM provided by Promocell (Catalog #C-12810) have been isolated from the ventricles of the adult human heart as reported by Li, et al., (Human Cell Culture Vol V, “Primary Mesenchymal Cells”; 2001, page 103-124; Luwer Academic Publishers). The epicardium and endocardium are removed and the tissue is mechanically and enzymatically digested. The cell suspension is then plated to remove the easily adherent fibroblasts. The unplated cells, primarily cardiac myocytes and endothelial cells, are plated in a fresh dish. Only the spherical hCM adhere while the rod-shaped hCM are washed away. Further purification steps using anti-CD90 antibody and anti-CD31 antibody coated beads are carried out during subculture. The hCM obtained from Promocell are sub-cultured in specialized myocyte growth media and used at passages 4 to 9 (media from Promocell, #C-22070+C-39275). Cells are defrosted according to package instructions and plated in tissue culture flasks. The cells adhere most predictably when plated at a density of at least 10,000 cells per square centimeter. The cells are passaged at 80-90% confluency. To passage, cells are rinsed once with HBSS (Gibco, Life Technologies Corp., #14170) at 100 μL/cm² of flask surface, incubated in TrypLE (Gibco, Life Technologies Corp., #12605) at 100 μL/cm² until rounded, then gently dislodged by rapping the side of the flask (e.g., as by a sharp blow or knock). An equal volume of media is added and the cells are transferred to a conical tube, centrifuged at about 200 g for 4 minutes and then resuspended in fresh media and plated. At least 96,000 cells are plated per 35 mm tissue culture dish and grown to confluency for use in the assay. Typically, the cells are incubated for about 5 days after passaging before reaching confluency.

Stock compounds are dissolved in either DMSO or 0.02N aqueous HCl at concentrations of 10 mM or 100 mM. A single compound is tested at 8 half-log dilutions in each experiment (final DMSO concentration less than 1%). The dilutions are prepared in aqueous media and warmed to 37° C. The range of concentrations chosen for the 8-point dilution are based on the IC₅₀ value from the biochemical assays. ANP (Tocris Bioscience, #1906) is made into a 100 mM stock solution in water and stored at −80° C. All reagents for the cGMP assay are from Cayman Chemical Co., Ann Arbor, Mich. (Cyclic GMP EIA Kit #581021).

Once the cells are grown to confluency, each dish is pretreated with either vehicle or compound for 30 minutes. Then, the cells are stimulated with 100 nM ANP or vehicle for 5 minutes. In each experiment, all 8 concentrations of compound are tested in duplicate and paired with ANP stimulation, while the controls, ANP alone and compound at the highest concentration alone, are tested once. Following treatment, the media is removed, replaced with 5% trichloroacetic acid (TCA), and the cells are placed on ice. The cells are immediately scraped in the TCA, transferred to Eppendorf tubes, sonicated and returned to ice. The precipitated protein is separated by centrifuging at 15,000 g for 20 minutes at 4° C. Cyclic nucleotides are retained in the supernatant. The TCA is removed from the supernatant using ether extraction (three washes with ethyl ether at 5× volume). The cleaned supernatants are dried in a vacuum centrifuge at room temperature and resuspended in 100 μL of ELISA assay buffer. Both the samples and the cGMP serial diluted standards are acetylated using 0.64M potassium hydroxide and 4% acetic anhydride to increase affinity of the cGMP antibody. Each of the 18 samples is tested in duplicate in the pre-coated assay plate alongside the 8-point cGMP standard dilutions. In addition, blank, maximum binding (B₀) and non-specific binding wells are included. To all wells containing 50 μL sample or standard, equal volumes of acetylcholinesterase-linked cGMP and cGMP antibody are added. The plate is incubated at 4° C. for 18 hours. The wells are then washed five times with wash buffer. Detection reagent containing acetylthiocholine and 2-nitrobenzoic acid is added and the plate is incubated at room temperature until the OD of the B₀ wells is at least 0.6 as recorded by the SoftMax 4.8 software (Molecular Devices, Sunnyvale, Calif.).

Each data point is converted to % B/B₀ (100*[(sample or standard OD−average non-specific binding)/(average B₀−average non-specific binding)]). The standards are plotted and fit to a 4-parameter logistic equation, and the concentrations of the samples are interpolated from the standard curve using Microsoft Excel and GraphPad Prizm. Values of cGMP levels are plotted against the logarithm of the concentration of compound, and the plot is fitted with a 4-parameter logistic equation (Y=Min+(Max−Min)/(1+10{circumflex over ( )}((Log EC50−X)*HillSlope))). The Min value is constrained to the value of the ANP response in the absence of compound.

Selected PDE1 inhibitory compounds embraced by the Invention show activity in the assay described. For example, the compound disclosed as Example 20 of U.S. Pat. No. 8,273,750 shows considerable augmentation of the cGMP response to ANP, as shown in FIG. 1. In addition, as shown in FIG. 3, the cGMP response resulting from Example 20 of U.S. Pat. No. 8,273,750 is considerably greater than the response resulting from the PDE5 inhibitors Sildenafil and Tadalafil.

Example 4: Macrophage Cellular Inhibition Assay Method for PDE1

Additional experiments conducted using selected PDE1 inhibitors in an HL60 macrophage cell line (American Type Culture Collection) show that there is a synergistic effect between ANP and PDE1 inhibition. HL60 cells were grown, differentiated and harvested as described previously (see Bender, A T, and Beavo, J A, 2006, PNAS 103, 460-465). The cells were grown in HEPES buffered RPMI 1640 medium with penicillin, streptomycin, and 10% fetal bovine serum. Phorbol-12-myristate-13-acetate (PMA), at 100 nM for 3 days, was used to differentiate the HL60 cells into macrophage-like cells. Following differentiation, the cells were incubated with a PDE1 inhibitor or vehicle (DMSO) beginning at time 0. At 40 minutes, 5 μM ionomycin was added. At 50 minutes, 100 nM ANP was added. At 60 minutes, the cells were harvested. Total cGMP levels were measured using a competitive ELISA (Bender and Beavo, 2006).

Using the PDE1 inhibitor disclosed as Example 20 of U.S. Pat. No. 8,273,750, it is found that the cGMP level induced in the HL60 cells by treatment with 100 nM ANP in combination with 100 nM of the PDE1 inhibitor is greater than that induced by either the ANP alone or the PDE1 inhibitor alone, as shown in FIG. 2. In addition, it can be seen that the cGMP level attained by co-treatment with ANP and the compound of Example 20 is much greater than that obtained by co-treatment with ANP and the mixed PDE1/PDE5 inhibitor SCH 51866 (used at 5 μM). In this experiment, the calcium ionophore ionomycin (used at 5 μM) was used to raise the intracellular calcium level and to counteract the cGMP rise induced by ANP. The decreasing cGMP signal caused by the activation of PDE1 by ionomycin is synergistically prevented by the combination of a PDE1 inhibitor and sub-optimal levels of ANP. Addition of ionomycin had only a weak cGMP lowering effect when combined with ANP and Example 20 treatment.

Example 5: Pharmacokinetic Analysis (Blood/Plasma Ratio)

Animals: Male, C57BL/6 mice (Jackson Labs, 25-30 g in body weight) are provided by Jackson Laboratories. Up to five mice are housed per cage and are maintained under a 12 hour light/dark cycle with access to food and water ad libitum. All procedures for the handling and use of animals follow the guidelines of the Institutional Animal Care and Use Committee (IACUC) of Columbia University, in accordance with NIH guidelines. Eight week-old mice (N=3/dose level or treatment group) are used in the experiments.

Experimental Treatment: Compounds: Selected compounds are evaluated in the present study. Formulation/Vehicle: 3% 1N HCl, 5% Labrasol and 92% of 5% TPGS in 0.05M Citrate buffer (CB, pH 4.0). The test compound(s) are prepared as solution in vehicle and are dosed in a volume of 8 ml/kg.

Compound Preparation: Powdered stocks of the test compound(s) are measured and dissolved in 3% 1N HCl, 5% Labrasol and 92% of 5% TPGS in 0.05M Citrate buffer (CB, pH 4.0). Two or three layers of 3 mm glass beads are added to the bottom of the 10 ml glass tube to promote mixing. The tube is mixed using a benchtop vortex mixer then sonicated using a VWR sonicator (model 750) for about 5 min until the drug powder is totally dissolved in into a vehicle solution.

Treatment of Animals: Mice (N=3 mice/dose/time point) receive a 10 mg/kg oral (PO) dose of the test compound(s) at time 0. Groups of mice are killed at a specified time point, either 0.25, 0.5, 1, or 2 h after drug administration. Brain tissue is collected and frozen at −80° C., until analysis. Blood is collected from the mice by puncture of the retro-orbital vein using a Pasteur pipette (VWR, Cat#53283-911), then deposited into silicon-coated blood collection tubes containing 0.105M sodium citrate solution (BD Vacutainer, #366392, Franklin Lakes, N.J.). Blood samples are centrifuged at the speed of 8000 g for 40 minutes in 4° C. (TOMY, refrigerated benchtop microcentrifuge, Fremont, Calif. 94583) and plasma decanted into Eppendorf tubes and frozen at −80° C. until analysis. Plasma and brain tissue samples are processed and analyzed by the analytical group using LC-MS/MS methods, as described below.

Sample Preparation: Samples of plasma are prepared for analysis as follows: 50 μL of the plasma samples is transferred into a 500 μl polypropylene microtube (Eppendorf Cat#022363611) as follows:

Standards Samples 50 μL control (blank) plasma 50 μL test sample plasma 10 μL standard working solution 10 μL 1:1 Methanol:Water in 1:1 Methanol:Water 150 μL 0.1 μM Reference 150 μL 0.1 μM Reference Compound in Methanol Compound in Methanol

Each tube is vortex mixed, then centrifuged for 20 min at 15000 rpm. The supernatant is collected and 100 μL of each is then transferred into a 96-well polypropylene Elisa plate for mass spectrometric analysis.

Samples of brain homogenate were prepared for analysis as follows: Approximately 0.5 g of brain tissue is weighed and homogenized with 1 mL Milli-Q water. Then 60 μL of the resulting homogenate is then transferred into a clean 500 μL polypropylene microtube (Eppendorf Cat#022363611) and treated as shown below:

Standards Samples 60 μL control (blank) brain 60 μL test sample brain homogenate homogenate 20 μL standard working solution 20 μL 1:1 Methanol:Water in 1:1 Methanol:Water 180 μL 0.1 μM Reference 180 μL 0.1 μM Reference Compound in Methanol Compound in Methanol

Each tube is vortexed, then centrifuged for 20 min at 15,000 rpm using a Tomy benchtop centrifuge at 4° C. 150 μL of each supernatant is then transferred into a 96-well plate for mass spectrometric analysis. Any remaining plasma or homogenate is stored at approximately −20° C. pending any necessary repeat analysis. For each test sample, a calibration curve is prepared covering the range of 0.5-500 ng/mL.

HPLC and Mass Spectrometric Analysis: Analysis to quantify the concentration of each compound in plasma and brain homogenate is carried out using reverse phase HPLC followed by mass spectrometric detection using the parameters listed:

HPLC: Waters Alliance 2795 HT

Mobile phase A: 0.1% Formic acid in water

Mobile phase B: 0.1% Formic acid in methanol

Column: Phenomenex Synergi 4 Fusion-RP 50×2 mm

Column Temperature: 40° C.

Time (min) Solvent A (%) Solvent B (%) Flow Rate (mL/min) 0 80 20 0.6 2 0 100 0.6 4 0 100 0.6

Waters Alliance 2795 LC rapid equilibration flow (mL/min): 5

Waters Alliance 2795 LC rapid equilibration time (min): 0.25

Re-equilibration time (min): 1

Injection volume (al): 10

Each compound is detected and quantified using Multiple Reaction Monitoring (MRM) of positive electrospray mode with a Waters QuattroMicro™ mass spectrometry system.

RESULTS: Plasma and Brain Analysis: Standard curves are established prior to the analysis of the samples and proved linear over the range of 0.5-1500 ng/mL in plasma and 0.5-500 ng/mL in brain. Plasma and brain levels of each compound are determined and expressed as means±standard deviation for each compound at each time point. Brain and plasma C_(max) and T_(max) values are estimated for each compound by visual inspection of the data. A ratio of brain/plasma concentration (B/P) is also calculated for each compound by dividing Brain AUC_((0-2h))/Plasma AUC_((0-2h)). 

What is claimed is:
 1. A combination of an NEP inhibitor with a PDE1 inhibitor, wherein the PDE1 inhibitor is a compound according to Formula VII:

wherein (i) X is methylene; (ii) Y is phenylene; (iii) Z is heteroaryl, halo, haloC₁₋₆alkyl, or —C(O)R¹ optionally containing at least one atom selected from a group consisting of N or O, wherein said Z is optionally substituted with halo; (iv) R¹ is C₁₋₆alkyl, haloC₁₋₆alkyl, —OH or —OC₁₋₆alkyl; (v) R⁴ is H and R⁵ is phenyl optionally substituted with one or more halo; in free or pharmaceutically acceptable salt form; and wherein the NEP inhibitor is selected from sampatrilat, fasidotril, Z13752A, MDL 100240, BMS 189921, LBQ657, AHU-377, and mixanpril, in free or pharmaceutically acceptable salt form.
 2. The combination of claim 1, wherein the PDE1 inhibitor is selected from any of the following

in free or pharmaceutically acceptable salt form.
 3. The combination of claim 1, wherein the PDE1 inhibitor is:

in free or pharmaceutically acceptable salt form.
 4. The combination of claim 1, wherein the NEP inhibitor is AHU-377 in free or pharmaceutically acceptable salt form.
 5. The combination of claim 1, wherein the NEP inhibitor is LBQ657 in free form or in the form of any pharmaceutically acceptable salt.
 6. A pharmaceutical composition comprising the combination of a PDE1 inhibitor and an NEP inhibitor according to claim 1, in further combination or association with a pharmaceutically acceptable diluent or carrier. 